The Health Risks of Extraterrestrial Environments
Skip Navigation...
  1. Home
  2. THREE Encyclopedia
  3. Bibliography
  4. Multimedia
  5. Archive
  6. Glossary

This site requires the use of
Adobe Acrobat Reader.
If you need to upgrade click the
icon below.

This site requires the use of Adobe Acrobat Reader. 
                    If you need to upgrade click the 
                    icon below.

Welcome to The Health Risks of Extraterrestrial Environments (THREE), an encyclopedic site whose goal is to present a discussion of the space radiation environment and its health risks to humans. The intent is to make this a good starting point for researchers new to either space, radiation, or both; a source of useful information for established investigators; and a teaching tool for students.

There are links across the top of the website to six distinct pages including the Home page you are reading.

The Encyclopedia link leads to a set of articles covering all aspects of space radiation concern, as well as an introduction to each topic. Early articles contain, in Flash format, slides that were presented to students of the NASA Space Radiation Summer School. Later articles have been written by investigators active in the relevant research area and have been peer reviewed under supervision of an associate editor. These articles may be viewed in PDF format. Click on Recent Articles below for a list of the most recent postings.

Citations to reports and to articles published in the scientific literature, that the associate editors consider to be of interest to the space radiation community, are listed monthly, together with a brief description by one of the article authors in most cases. The current month's listing may be accessed by clicking on the Current Research Citations link below. These citations are collected and archived on the Bibliography page, sorted by Encyclopedia topics, as a living bibliographic complement to the encyclopedia articles.

Reviews of recently published books on topics related to space radiation may be found under the Book Reviews link below. General news items of interest to the THREE community are listed under the In the News link below.

A few important topics are collected in the Multimedia page; future material will be added as appropriate.

The Archive is a repository of material kept for reference; the site contains records documenting the history of the NASA Space Radiation Summer School, as well as information from prior Space Radiation Investigators’ Workshops and a history of Featured Articles previously featured under the Featured Article link below.

Finally, a glossary of terms related to space radiation research is available on the similarly named page.

The THREE Editorial Board is responsible for oversight of the content and policies for this site. It is hosted by the NASA Johnson Space Center.

Contributions to any part of THREE, especially submissions for articles, are welcome; instructions for authors are posted in the Statement of Policies. Please send your comments and contributions along with your contact information to the THREE Page Editor.

Walter Schimmerling
THREE Chief Editor

Carol A. Mullenax
THREE Page Editor

  • Track structure and the quality factor for space radiation cancer risk (PDF) Dudley T. Goodhead

    Correction Posted September 28, 2018

  • Abortive apoptosis and its profound effects on radiation‐, chemical‐, and oncogene induced carcinogenesis (PDF) Xinjian Liu, Ian Cartwright, Fang Li, and Chuan-Yuan Li

    Posted June 21, 2018

  • Using Proteomics Approaches to Assess Mechanisms Underlying Low Linear Energy Transfer or Galactic Cosmic Radiation-Induced Cardiovascular Disease (PDF) Zachary D. Brown, Muath Bishawi, and Dawn E. Bowles

    Posted May 21, 2018

  • The Emerging Role of Exosomes in the Biological Processes Initiated by Ionizing Radiation (PDF) Munira A Kadhim, Scott J Bright, Ammar H J Al-Mayah, and Edwin Goodwin

    Posted April 11, 2018

  • Solar Particle Events and Radiation Exposure in Space (PDF) Shaowen Hu

    Posted March 31, 2017

  • An introduction to space radiation and its effects on the cardiovascular system (PDF) Marjan Boerma

    Posted October 13, 2016

  • Precise Genome Engineering and the CRISPR Revolution (Boldly Going Where No Technology Has Gone Before.) (PDF) Eric A. Hendrickson

    Posted April 6, 2016

Track structure and the quality factor for space radiation cancer risk (PDF) Dudley T. Goodhead
A major risk from exposure to space radiation is the induction of cancer and it is from estimates of this risk that the maximum career flight times of NASA space crew members are restricted by a permissible exposure limit. For the purpose of demonstrating compliance with the career limit, NASA has developed a cancer risk projection model for radiation exposure induced death from cancer (REID), in which the formulation and numerical values of the quality factor (QFNASA) are substantially different from those of the quality factor (Q) or radiation weighting factor (wR) routinely applied for radiation protection on earth. The quality factor is used to account for the increased effectiveness of radiations of high linear energy transfer (LET), compared to the effectiveness of low-LET γ-rays derived from epidemiological studies of the atomic-bomb survivors. The need for a special approach for space radiation is dictated by the special characteristics of the charged particles from solar radiation and especially the charged particles of high energy and charge (HZE) in galactic cosmic rays (GCR). This article considers aspects of radiation track structure in relation to the relative biological effectiveness (RBE) of HZE particles and the quality factor used for space radiation. The NASA quality factor (QFNASA) is composed of two terms, which can be interpreted as broadly representing the low- and the high-ionization-density components of the HZE particle tracks. These are discussed in turn as they relate to available experimental evidence on the biological effectiveness of such components. Also briefly described are subsequent published proposals for a reformulation of the quality factor to relate more directly to the acute γ-ray exposures from the atomic bombs and for further refinement of the parameter values (and their uncertainties) that determine the shape of the quality factor function. Other recent developments are also mentioned.

Illustration of features commonly observed for the variation of relative biological effectiveness (RBE) with LET.  (Adapted from Goodhead 1994.)

Donald V. Reames: “Solar Energetic Particles: A Modern Primer on Understanding Sources, Acceleration, and Propagation” (Springer, 2017). (PDF); reviewed by Stephen Kahler.

International Astronautical Congress

The 70th annual International Astronautical Congress (IAC). #IAC2019, hosted by the American Institute of Aeronautics and Astronautics – AIAA will take place in Washington D.C., United States from 21 – 25 October 2019. An intense week during which all space players will gather to discuss the advancement and progress of space in its various features; in particular this year, the IAC will commemorate that “one giant leap for mankind”: the 50th anniversary of a feat once thought impossible: humans walking on the moon, and celebrate the international accomplishments and partnerships that have become the hallmarks of space exploration.

IAC 2019 will involve everyone offering a rich program of Plenaries, Highlight Lectures, Technical Lectures as well as a Global Networking Forum and many social events abundant in networking opportunities.
Return to top

7th International Systems Radiation Biology Workshop

The 7th International Systems Radiation Biology Workshop will be held September 28-30, 2019, at the Institute of Environmental Systems Biology, Dalian Maritime University, in Dalian, China.

This workshop will bring together leading investigators from the China, US, Japan, European Union and other countries to discuss how new methodologies can be utilized for space radiation risk assessment and mitigation research. The workshop topics include but are not limited to omics approaches in system radiation biology, radiation induced genetic and epigenetic changes, individual radiation sensitivity and radiation risk assessment, and systems approaches to disease modeling and treatment on Earth and in space.

Deadline for abstract submission has passed.
Return to top

AIR2 (Access to INFRASTRUCTURES for Radiation protection Research)

The June 2019 issue of the AIR2 Bulletin has articles on ESA support of ground-based radiobiology research for space radiation protection, featuring Dr. Jennifer Ngo-Anh – SciSpacE Team Leader - Directorate of Human and Robotic Exploration Programmes (HRE-RS), European Space Agency and the FAIR (Facility for Anti-protons and Ion Research), upgrading the heavy ion accelerators at the Helmholtz Institute in Darmstadt, Germany. To be added to their mailing list, contact Maria Panagiotopoulou at
Return to top

2019 WRMISS meeting

The next meeting of the Workshop on Radiation Monitoring for the International Space Station (WRMISS) has been scheduled in Athens, Greece, September 3-5, 2019. WRMISS is an annual meeting to discuss the scientific definition of an adequate radiation monitoring package and its use by the scientific community on the ISS. Types of instruments and research topics need to be defined in order to optimize the radiation safety of the ISS crew. For further questions please contact the chairman of the workshop Dr. Günther Reitz ( at the German Aerospace Center (DLR). Further information on these meetings can be found at the organization website,
Return to top

TRISH Red Risk School

The Translational Institute for Space Health (TRISH) held the second "Red Risk School" 18-22 March 2019, offering a set of virtual workshop sessions to help inform potential proposers for NASA and TRISH research solicitations about the highest priority (or "red") risks identified by the NASA’s Human Research Program (HRP).

The March 2019 sessions were recorded and are posted to the TRISH website for ongoing viewing availability, alongside the first set of workshop sessions from April 2018.

With TRISH’s focus on innovation and synergy, this is a perfect opportunity for non-traditional researchers new to NASA to get a crash course in the HRP high priority risks. If you are interested in finding out more about the Red Risk School, visit TRISH’s website at

Return to top

ESA and FAIR establish joint Summer School

The European Space Agency (ESA) and the international accelerator center FAIR (Facility for Antiproton and Ion Research), which is currently being built at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, will establish a joint Summer School for Radiation Research. Just over a year ago, ESA and FAIR signed a cooperation agreement on cosmic radiation research. The Summer School is a direct result of the joint activities of the two partners agreed at the time.

The Summer School will be held at ESA´s European Space Operations Centre ESOC as well as at the GSI/FAIR campus in order to train students in basic heavy ion biophysics for both terrestrial applications (e.g. medical therapies) and space applications (e.g. space radiation detection, monitoring and protection). The program includes lectures from experts in the field, site visits to facilities in Darmstadt and practical training and research opportunities at GSI/FAIR. The students also have the possibility to develop their own experiment ideas, using available beamtime at GSI accelerators.

Up to 15 Ph.D. students and postdocs from various radiation-related disciplines will be accepted. Eligible participants must be from an ESA Member State, with a few spots available to international students. Preliminary dates for the summer school are 15 September – 1 October.
Return to top

Blakely is 20th Gray Medal Recipient

The International Committee on Radiation Protection has announced that the Twentieth Gray Medal will be presented to Dr. Eleanor Blakely at the 16th International Congress of Radiation Research in Manchester, UK, in August 2019.

Since 1989, Dr. Blakely has been a Senior Staff Biophysicist at the Lawrence Berkeley National Laboratory (LBNL) working directly with Professor Cornelius Tobias and with Drs. Joseph Castro and Theodore Phillips conducting pre-clinical investigations, and Phase I/II trials with heavy charged particle radiotherapy, and studying the basic mechanisms of radiation responses, with an emphasis on charged particle radiation effects. Her professional activities include service on a variety of advisory panels for several hospitals, universities, and numerous federal agencies. In 2000 she was elected to the National Council on Radiation Protection and Measurements (NCRP) and served on Scientific Committee (SC) 75 that produced NCRP Report No. 132, Radiation Protection Guidance for Activities in Low-Earth Orbit; and SC 1-7 that produced NCRP Report No. 153, Information Needed to Make Radiation Protection Recommendations for Space Missions Beyond Low-Earth Orbit. She also was the 2007-2008 Scientific Director of the NASA Space Research Summer School. Dr. Blakely is one of the Principal Investigators of the Galactic Cosmic Ray Simulation Consortium, conducting research to validate radiation risk predictions at the NASA Space Radiation Laboratory.

Her colleagues at NASA are pleased with this well-deserved recognition of a longtime NASA investigator and convey their congratulations.
Return to top

James M. Slater, MD

James M. Slater, MD, who pioneered the world’s first hospital-based proton treatment center at Loma Linda University Health, died December 26, 2018. He was 89. He is survived by his wife of 70 years, Mary JoAnn Strout, and by his five children, Jim, Julie, Jan, Jerry, and Jon, 14 grandchildren, and 18 great-grandchildren. He was a devoted husband and father.

James Munroe Slater was born in 1929 in Salt Lake City, Utah. He graduated from the University of Utah, in 1955 with a bachelor’s degree in physics, and obtained his M.D. from the Loma Linda University School of Medicine in 1963. He trained as a resident at both LDS Hospital in Utah and White Memorial Medical Center in Los Angeles and completed a National Institutes of Health Fellowship at University of Texas MD Anderson Cancer Center. He accepted the invitation to return to Loma Linda University Health in 1970 and chaired the Department of Radiation Medicine at Loma Linda University for more than 20 years.

The James M. Slater, M.D. Proton Treatment and Research Center — which opened in 1990 — has since treated more than 18,000 patients from around the world. When the Loma Linda University Medical Center Proton Treatment Center opened in 1990, it was the only place in the world to offer proton therapy for patient treatment and research in a hospital setting. It would remain the only hospital-based treatment center of its kind in the United States until 2003. In 2007, it was renamed the James M. Slater, M.D. Proton Treatment and Research Center in his honor. Today there are approximately 25 proton therapy centers in operation, with another 11 centers under construction or in development, according to the National Association for Proton Therapy. Slater described the compassion he felt for his patients in a documentary, The Convergence of Disciplines. During his residency training in radiology, he said, “[It] was a shocking experience to see how ill we made our patients. During treatment they became very, very sick. Some of them had to stop treatment and recuperate for a week or so before they could come back. This reduced their chance for a cure and caused misery for them as an individual and for their family.”

Slater also maintained an enthusiastic interest in space radiation problems. He enjoyed telling the story of how he had lunch with one of us (WS) in the basement restaurant of the Hamburg City Hall, where we both were attending the 30th Scientific Assembly of the Committee for Space Research (COSPAR), in July 1994 and we realized that NASA and Loma Linda had essentially complementary interests.

At the time, NASA was seriously concerned about access to a charged particle accelerator capable of simulating the space radiation environment. The only particle accelerator capable of delivering the full spectrum of particles present in space, the Berkeley BEVALAC, was shut down by DOE, and budget for NSRL had not yet been approved. LLU beams were capable of providing some of the knowledge required, especially with relation to solar particle events whose major impact is on EVAs.

LLU had established a superb clinical facility, but needed to develop the research capability required to provide a scientific basis for treatment planning. The relevant radiobiology has significant overlap with the radiation biology required to predict the risks to astronauts exposed to space radiation.

Accordingly, as a result of this conversation, Slater and Schimmerling initiated a Memorandum of Agreement between NASA and Loma Linda University, concerning cooperation in radiation biology and physics and their application to medicine. It was signed, in December 1994, by Joan Vernikos, Director of the NASA Life and Biomedical Sciences and Applications Division, and by David B. Hinshaw, Sr. President, Loma Linda University Medical Center, with the Loma Linda Congressional Representative, the Hon. Jerry Lewis, attending. The main objectives of this MOA were to provide access to accelerated proton beams and related research laboratories for NASA-sponsored investigators; provide for contribution of NASA-sponsored investigators to the academic and educational programs of LLU; and, to facilitate transfer of technical expertise between NASA and LLU in areas of radiation physics and radiation biology.

These objectives were achieved, as LLU has provided, and continues to provide, beams for NASA investigators, including a successful series of studies of space suits. A major contribution has also been coordination between LLU and NSRL hardware, so that experiments can be conducted at either laboratory using the same irradiation equipment. LLU has achieved a credible research capability, as evidenced by successful competition for NASA research grants by their scientists. The LLU Medical Center and investigators working there continue to make significant contributions to the NASA Space Radiation Program Element under the guidance of Nelson, who was recruited from the Jet Propulsion Laboratory and who led the early development of the current LLU research capability.

None of this would have been possible without the determination of a soft-spoken, gentle, modest man of far-reaching vision, James Slater. He was a visionary, a pioneer, and a medical and scientific leader. He was also, I am humbly proud to say, a teacher and a friend. He will be sorely missed.

Walter Schimmerling
Gregory A. Nelson

Return to top

Funding Opportunity for Development of Radiation/Nuclear Medical Countermeasures

The National Institute of Allergy and Infectious Diseases (NIAID) has released a Broad Agency Announcement soliciting proposals for “Development of Radiation/Nuclear Medical Countermeasures.”

Solicitation Number: HHS-NIH-NIAID-BAA2019-1
Agency: Department of Health and Human Services
Office: National Institutes of Health
Location: National Institute of Allergy and Infectious Diseases

The goal of this research is to support the development of safe and effective Medical Countermeasures (MCMs) to mitigate and/or treat tissue injuries exposure to ionizing radiation from a radiological or nuclear incident, thereby leading to a reduction in radiation-associated morbidities and mortalities. Given the extent of damage sustained after a mass casualty incident, drugs are not expected to be mobilized from the Strategic National Stockpile (SNS) before 24 hours, hence the need for MCMs that are efficacious 24 hours or later post-exposure.
Return to top

NCI Course on Radiation Epidemiology and Dosimetry

The National Cancer Institute is conducting a course on Radiation Epidemiology and Dosimetry to be taught at NCI Shady Grove, 9609 Medical Center Drive, Rockville, MD, from September 9-12, 2019. This is a free course for those who are interested in learning about the health effects of radiation exposure.

Email to be added to the notification list.
Return to top

Summer 2019 radiation modelling course in Pavia, Italy

A course will be offered in Pavia, Italy, from May 27th to June 7th, 2019 entitled "Modelling radiation effects from initial physical events: Learning modelling approaches and techniques in radiation biophysics and radiobiology research, from basic mechanisms to applications."

The course is open to students (e.g. MSc, PhD and specialization students), young investigators, continuing professional education, in particular with interest in scientific disciplines related to: Radiation Biophysics, Radiobiology and Radiation protection.

There is no course fee. A limited number of free lodgings in Pavia colleges will be available. No financial support will be provided. People wishing to apply should submit preferably by email the following documents

  • A letter of application
  • A CV with a description of the scientific career
  • A supporting letter from the supervisor/head of laboratory

to the Directors of the course: Andrea Ottolenghi and Giorgio Baiocco Dipartimento di Fisica Università degli Studi di Pavia Via Bassi 6 I-27100 Pavia, Italy; and, with copy to

Deadline for applications is April 15th, 2019.
Return to top

Announcing the new Big Data to Knowledge (BD2K) Resources Page

Big Data to Knowledge (BD2K) grantees developed a series of resources for the biomedical research and data science communities to use big data to answer biomedical research questions. Under current efforts to make the products of BD2K research usable, discoverable, and disseminated to the biomedical research community, the NIH Office of Strategic Coordination (OSC) released a webpage with direct hyperlinks to the resources developed through BD2K funding (

The BD2K resource page will be updated periodically and populated with new resources as they become available. Please feel free to share this information with interested colleagues.
Return to top

Low Dose Rate Neutron Irradiator Facility

The Low Dose Rate Neutron Irradiator Facility at Colorado State University (CSU) provides NASA investigators with the capability of exposing mice and rats to chronic neutron irradiation, which has high LET effects. Currently, simulating continuous exposures to space radiation over time periods of months to years is not technical feasible in accelerator facilities. However, continuous exposures to fission spectrum neutrons are possible, and there are physical and biological commonalities between the effects of neutrons and HZE ions that make neutron irradiation a meaningful surrogate for space radiation exposures.

The Neutron Irradiator Facility is located on the CSU Foothills Campus in Fort Collins, Colorado. It is a rodent vivarium with a capacity of up to 900 mice and 60 rats that houses a neutron irradiator with a 252Cf neutron source. The animals are irradiated at a dose rate of 1 mGy/day, with a day consisting of about 20 hours with the 252Cf source exposed (irradiation) and the remaining 4 hours with the source shielded so that personnel can enter the facility for animal care and husbandry. Because 252Cf undergoes radioactive decay, the actual daily exposure time depends on the activity of the source. Total radiation times can be up to the lifespans of the animals. Photons deliver 20% of total dose. The dose averaged LET is 68±8 keV/um. Total dose rates are within ±10% throughout the distribution of cages and racks.

For information on using the CSU Low Dose Rate Neutron Irradiator Facility, contact Dr. Mike Weil at

Interior view of the facility showing the neutron irradiator (blue with yellow attenuator) surrounded by racks hold mouse and rat cages.
Interior view of the facility showing the neutron irradiator (blue with yellow attenuator) surrounded by racks hold mouse and rat cages.
Return to top

Advances in space radiation physics and transport at NASA.
Norbury JW, Slaba TC, Aghara S, Badavi FF, Blattnig SR, Clowdsley MS, Heilbronn LH, Lee K, Maung KM, Mertens CJ, Miller J, Norman RB, Sandridge CA, Singleterry R, Sobolevsky N, Spangler JL, Townsend LW, Werneth CM, Whitman K, Wilson JW, Xu SX, Zeitlin C. Life Sci Space Res. 2019 Jul 10. [Article in Press] Review. [7/31]
This paper describes significant new discoveries and advances made in space radiation physics and transport over the past decade. Some of the most important new developments include the following: 1) The discovery of a minimum in the dose-equivalent versus depth curve; 2) A large contribution to dose from pions; 3) A large contribution of neutrons and light ions to dose equivalent for realistic shield thickness; 4) A realization that there are large and significant gaps in cross section measurements needed for space radiation; 5) Development of 3-dimensional deterministic transport methods; 6) Development of a fully relativistic nuclear fragmentation model; 7) Development of a GCR simulation capability at the NASA Space Radiation Laboratory; 8) Development of an On-Line Tool for the Assessment of Radiation In Space (OLTARIS); 9) Development of a Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model. Each of these advances contribute significantly to improving our knowledge of space radiation and will help achieve safer long term space travel. The paper is coauthored by 22 scientists from various NASA centers, universities and commercial companies, and includes work funded by NASA’s Human Research Program and Advanced Exploration Systems.
Return to top

Update on Galactic Cosmic Ray Integral Flux Measurements in Lunar Orbit With CRaTER
Zeitlin C, Schwadron NA, Spence HE, Jordan AP, Looper MD, Wilson J, Mazur JE, Townsend LW. Space Weather. 19 June 2019:17. [7/30]
We report measurements of increasing intensities of Galactic Cosmic Ray protons and helium ions from 2015 through the end of 2018. The overall decrease in solar activity in this period has led to an increased flux of energetic particles, to levels that are approaching those observed during the previous solar minimum in 2009/2010, which was the deepest minimum of the Space Age. The data have implications for human exploration of deep space, and may provide useful benchmarks for models of cosmic ray fluxes as a function of solar modulation.
Return to top

Dose, LET and Strain Dependence of Radiation-Induced 53BP1 Foci in 15 Mouse Strains Ex Vivo. Introducing Novel DNA Damage Metrics
Penninckx S, Cekanaviciute E, Degorre C, Guiet E, Viger L, Lucas S and Costes SV. Radiation Research, 2019:192;1-12. [7/23]
A comprehensive comparative analysis on the repair of radiation-induced DNA damage ex vivo in 15 strains of mice, including 5 inbred reference strains and 10 collaborative-cross strains, of both sexes, totaling 5 million skin fibroblast cells imaged by three-dimensional high-throughput conventional microscopy. Non-immortalized primary skin fibroblasts derived from 76 mice were subjected to increasing doses of both low- and high-LET radiation (X rays; 350 MeV/n 40Ar; 600 MeV/n 56Fe), which are relevant to carcinogenesis and human space exploration. All 15 strains showed the same dose and LET dependence, but strain differences were preserved under various experimental conditions, indicating that the number and sizes of repair domains are modulated by the genetic background of each strain.
Return to top

Effects of exposure to 12C and 4He particles on cognitive performance of intact and ovariectomized female rats.
Rabin BM, Miller MG, Larsen A, Spadafora C, Zolnerowich NN, Dell'Acqua LA, Shukitt-Hale B. Life Sci Space Res. 2019 Jul 10. [Article in Press] [7/15]
Exploratory class missions to other planets will include both male and female astronauts. Previous research has indicated that female subjects do not show a disruption of cognitive performance following exposure to HZE particles. Because estrogen can function as a neuroprotectant, the cognitive performance of intact and ovariectomized female rats with estradiol or vehicle implants was tested following exposure to 12C (290 MeV/n) or 4He particles (300 MeV/n). The results indicated that exposure to 12C or 4He particles did not disrupt operant performance in the intact rats. Estradiol implants exacerbated the disruptive effects of radiation on performance. Although estrogen does not appear to function as a neuroprotectant following exposure to space radiation, the data suggest that intact females may be less responsive to the deleterious effects of exposure to space radiation on cognitive performance, possibly due to the effects of estrogen on cognitive performance.
Return to top

What does radiation biology tell us about potential health effects at low dose and low dose rates.
Azzam EI. J Radiol Prot. 2019 Jun 19. [Epub ahead of print] [7/2]
The health risks to humans exposed to low dose and low dose rate ionizing radiation remain ambiguous and are the subject of debate. The need to establish risk assessment standards based on the mechanisms underlying low dose/low fluence radiation exposures has been recognized by scholarly and regulatory bodies as critical for reducing the uncertainty in predicting adverse health risks of human exposure to low doses of radiation. Here, a brief review of laboratory-based evidence of molecular and biochemical changes induced by low doses and low dose rates of radiation is presented. In particular, two phenomena, namely bystander effects and adaptive responses that may impact low level radiation health risks are discussed together with the need for further studies. The expansion of this knowledge by considering the important variables that affect the radiation response (e.g., genetic susceptibility, time after exposure), and using the latest advances in experimental models and bioinformatics tools, may guide epidemiological studies towards reducing the uncertainty in predicting the potential health hazards of exposure to low dose radiation.
Return to top

Radiation-induced DNA damage cooperates with heterozygosity of TP53 and PTEN to generate high grade gliomas
Todorova PK, Fletcher-Sananikone E, Mukherjee B, Kollipara R, Vemireddy V, Xie XJ, Guida PM, Story MD, Hatanpaa K, Habib AA, Kittler R, Bachoo R, Hromas R, Floyd JR, Burma S. Cancer Res. 2019 May 14. pii: canres.0680.2019 [Epub ahead of print] [6/20]
Using transgenic mouse models, this study uncovers mechanisms by which ionizing radiation, especially particle radiation, promotes the development of lethal brain cancers called glioblastoma. Of special relevance to long-distance space missions, the study clearly shows that high-LET heavy ions carry a much greater carcinogenic risk compared to low-LET protons or X-rays. Importantly, the paper describes a versatile mouse model that can be used in the future for the testing of countermeasures to prevent brain cancer development from radiation exposure.
Return to top

Changes in one-carbon metabolism and DNA methylation in the hearts of mice exposed to space environment-relevant doses of oxygen ions (16O)
Miousse IR, Skinner CM, Sridharan V, Seawright JW, Singh P, Landes RD, Cheema AK, Hauer-Jensen M, Boerma M, Koturbash I. Life Sci Space Res. 2019 August; 22, 8-15. [6/20]
Cardiovascular disease constitutes an important threat to humans after space missions beyond the Earth's magnetosphere. We investigated the effects of 16O on the cardiac methylome and one-carbon metabolism in male C57BL/6 J mice. Left ventricles were examined 14 and 90 days after exposure to space-relevant doses of 0.1, 0.25, or 1 Gy of 16O (600 MeV/n). DNA methylation in repetitive elements was elevated, particularly after 90 days, while expression showed first a decrease followed by an increase in transcript abundance. Metabolomics analysis revealed that metabolites involved in homocysteine remethylation, central to DNA methylation, were unaffected by radiation, but the transsulfuration pathway was impacted after 90 days, with a large increase in cystathione levels at the lowest dose.
Return to top

Positive impact of low-dose, high-energy radiation on bone in partial- and/or full-weightbearing mice
Bokhari RS, Metzger CE, Black JM, Franklin KA, Boudreaux RD, Allen MR, Macias BR, Hogan HA, Braby LA, Bloomfield SA. npj Microgravity. 2019 Jun 4;5(1):13. [6/10]
We provide evidence for persistent positive impacts of high-LET radiation exposure preceding a period of full or partial weightbearing on bone mass and microarchitecture in the distal femur and, for full weightbearing mice only and more transiently, cortical bone energy absorption values.
Return to top

Risks of cognitive detriments after low dose heavy ion and proton exposures
Cucinotta FA, Cacao E. Int J Radiat Biol. 2019 May 23. [Epub ahead of print] [6/5]
Purpose: Heavy ion and proton brain irradiations occur during space travel and in Hadron therapy for cancer. Heavy ions produce distinct patterns of energy deposition in neuron cells and brain tissues compared to X-rays leading to large uncertainties in risk estimates. We make a critical review of findings from research studies over the last 25 years for understanding risks at low dose.
Conclusions: A large number of mouse and rat cognitive testing measures have been reported for a variety of particle species and energies for acute doses. However tissue reactions occur above dose thresholds and very few studies were performed at the heavy ion doses to be encountered on space missions (<0.04 Gy/y) or considered dose-rate effects, such that threshold doses are not known in rodent models. Investigations of possible mechanisms for cognitive changes have been limited by experimental design with largely group specific and not subject specific findings reported. Persistent oxidative stress and activated microglia cells are common mechanisms studied, while impairment of neurogenesis, detriments in neuron morphology, and changes to gene and protein expression were each found to be important in specific studies. Future research should focus on estimating threshold doses carried out with experimental designs aimed at understating causative mechanisms, which will be essential for extrapolating rodent findings to humans and chronic radiation scenarios, while establishing if mitigation are needed.
Return to top

Fluence-to-effective dose conversion coefficients for male astronauts.
Timoshenko GN, Belvedersky MI. J Radiol Prot. 2019 Jun;39(2),511-21. [5/14]
The problem of the reliable estimation of astronauts' radiation exposure doses in deep space is very important and relevant in connection with the accepted space research programmes. The effective dose value based on ICRP Publication 103 presents too conservative an estimate of an astronaut's radiation risk. A more realistic dose can be calculated on the basis of relationships between the radiation quality factor and linear energy transfer or linear energy or Z*2/β 2, according to the NASA concept. In addition, it is reasonable to use a set of tissue weighting coefficients (normalised relative detriments) that have been averaged over a cohort of working age males similar to the male astronaut cohort. The closest to the male astronauts is the NASA cohort of males aged 30-60 years who have never smoked. The fluence-to-effective dose equivalent conversion coefficients calculated specially for male astronauts are compared. Different approaches to radiation risk estimation for astronauts are discussed.
Return to top

Current status of space radiobiological studies in China
Pei W, Hu W, Chai Z, Zhou G. Life Sci Space Res. 2019 May 8. [5/12]
After successfully launching two space laboratories, Tiangong-1 and Tiangong-2, China has announced her next plan of constructing the China Space Station (CSS) in 2022. The CSS will provide not only platforms for Chinese scientists to carry out experimental studies in outer space but also opportunities for open international cooperation. In this article, we review the development of China's manned space exploration missions and the preliminary plan for CSS. Besides, China has initiated space radiation research decades ago with both ground-based simulation research platform and space vehicles and has made noticeable progresses in several aspects. These include the studies for human health risk assessment using mammalian cell cultures and animals as models. Furthermore, there have been numerous studies in assessing the space environment in plant breeding.
Return to top

Thick target neutron yields from 100- and 230- MeV/nucleon helium ions bombarding water, PMMA, and iron
P. Tsai, L. Heilbronn, B. Lai, Y. Iwata, T. Murakami, R. Sheu. Nuclear Instruments and Methods in Physics Research B. 2019;449,62-70. [5/8]
The yields of secondary neutrons produced from 100- and 230-MeV/nucleon 4He ions, respectively, stopping in thick natFe, PMMA and water targets were measured. Double-differential thick target neutron yields, angular distributions, and total neutron yields per ion were benchmarked against model calculations with the PHITS, FLUKA, and MCNP Monte Carlo simulation codes. Our results indicate that significant improvements are needed in the physics models used to describe 4He-induced nuclear reactions for predictions of neutron production.
Return to top

Funding for radiation research: past, present and future
Cho K, Imaoka T, Klokov D, Paunesku T, Salomaa S, Birschwilks M, Bouffler S, Brooks AL, Hei TK, Iwasaki T, Ono T, Sakai K, Wojcik A, Woloschak GE, Yamada Y, Hamada N. International Journal of Radiation Biology. 2019;95,1-25. [4/30]
For more than a century, ionizing radiation has been indispensable mainly in medicine and industry. Radiation research is a multidisciplinary field that investigates radiation effects. Radiation research was very active in the mid- to late 20th century, but has then faced challenges, during which time funding has fluctuated widely. Here we review historical changes in funding situations in the field of radiation research, particularly in Canada, European Union countries, Japan, South Korea, and the US. We also provide a brief overview of the current situations in education and training in this field. A better understanding of the biological consequences of radiation exposure is becoming more important with increasing public concerns on radiation risks and other radiation literacy. Continued funding for radiation research is needed, and education and training in this field are also important.
Return to top

Research plans in Europe for radiation health hazard assessment in exploratory space missions.
Walsh L, Schneider U, Fogtman A, Kausch C, McKenna-Lawlor S, Narici L, Ngo-Anh J, Reitz G, Sabatier L, Santin G, Sihver L, Straube U, Weber U, Durante M. Life Sci Space Res. 2019 May;21,73-82. [4/26]
The European Space Agency (ESA) is currently expanding its efforts in identifying requirements and promoting research towards optimizing radiation protection of astronauts. Space agencies use common limits for tissue (deterministic) effects on the International Space Station. However, the agencies have in place different career radiation exposure limits (for stochastic effects) for astronauts in low-Earth orbit missions. Moreover, no specific limits for interplanetary missions are issued. Harmonization of risk models and dose limits for exploratory-class missions are now operational priorities, in view of the short-term plans for international exploratory-class human missions. The purpose of this paper is to report on the activity of the ESA Topical Team on space radiation research, whose task was to identify the most pertinent research requirements for improved space radiation protection and to develop a European space radiation risk model, to contribute to the efforts to reach international consensus on dose limits for deep space. The Topical Team recommended ESA to promote the development of a space radiation risk model based on European-specific expertise in: transport codes, radiobiological modelling, risk assessment, and uncertainty analysis. The model should provide cancer and non-cancer radiation risks for crews implementing exploratory missions. ESA should then support the International Commission on Radiological Protection to harmonize international models and dose limits in deep space, and guarantee continuous support in Europe for accelerator-based research configured to improve the models and develop risk mitigation strategies.
Return to top

Applied nuclear physics at the new high-energy particle accelerator facilities
Durante M, Golubev A, Park W-Y, Trautmann C. Physics Reports. 2019;800,1-37. [4/26]
New, large accelerator facilities are currently under construction in Europe, Asia, and USA. The upcoming facilities open new opportunities for research in biomedical applications, such as particle radiography, radioactive beam imaging, ultra-high dose rates and new ions for therapy. Moreover, space radiation research and materials science can successfully exploit these new centers. The new facilities can pave the way to many future applications of nuclear physics for the benefit of the society. In this paper we will summarize the current status of applied sciences at high-energy accelerators, describe the characteristics of some of the machines under construction (FAIR, NICA, RAON, ELI) and discuss the new opportunities offered by these facilities in applied sciences.
Return to top

The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight
Garrett-Bakelman FE et al. Science. 2019;364,eaau8650. [4/19]
The research is featured on the cover of the journal issue with the caption: "A study of identical twins identifies molecular, physiological, and cognitive changes specific to one twin who spent a year living aboard the International Space Station. The cover depicts the twins and their respective Earth-bound and space residencies, with a rocket and the International Space Station in the background."
Return to top

HMGB1 mediated autophagy protects glioblastoma cells from carbon-ion beam irradiation injury
Lei R, Yan L, Deng Y, Xu J, Zhao T, Awan MUF, Li Q, Zhou G, Wang X, Ma H., Acta Astronaut. 2019 Mar 19. [4/16]
The present study investigated autophagy changes and the expression of HMGB1 in human glioblastoma cells, responding to carbon-ion beam irradiation (35 keV/μm, 80.55 MeV/u). U251 cells were irradiated with carbon-ion beams and cell proliferation was measured by counting the number of living cells. A high level of autophagy was induced 24 h after irradiation with 1 Gy carbon ions and then decreased in a time- and dose-dependent manner. The expression of the whole HMGB1 showed correlation with the dynamic autophagic level. In summary, carbon-ion beam irradiation could elevate autophagy and HMGB1 expression efficiently, which would protect the cells from programmed cell death via autophagy. Apoptosis as measured by expression of caspase activities increased as the dose increased, which was accompanied with decreased levels of LC3B and HMGB1.
Return to top

TOPAS-nBio: An Extension to the TOPAS Simulation Toolkit for Cellular and Sub-cellular Radiobiology
Schuemann J, McNamara AL, Ramos-Méndez J, Perl J, Held KD, Paganetti H, Incerti S and Faddegon B. Radiat Res. 191, 125–138 (2019). [3/19]
The TOPAS Monte Carlo (MC) system provides detailed simulations of patient scale properties; however, the fundamental unit of the biological response to radiation is a cell. TOPAS-nBio is an extension of TOPAS that extends TOPAS to model radiobiological experiments. TOPAS-nBio is based on and extends Geant4- DNA. It explicitly simulates every particle interaction (i.e., without using condensed histories) and propagates radiolysis products. A graphical user interface offers full track-structure Monte Carlo simulations, integration of chemical reactions within the first millisecond, an extensive catalogue of specialized cell geometries as well as sub-cellular structures such as DNA and mitochondria, and interfaces to mechanistic models of DNA repair kinetics. Additionally, we expanded the chemical reactions and species provided in Geant4-DNA and developed a new method based on independent reaction times (IRT). Chemical stage simulations using IRT were a factor of 145 faster than with step-by-step tracking. The TOPAS- nBio extension to the TOPAS MC application offers access to accurate and detailed multiscale simulations, from a macroscopic description of the radiation field to microscopic description of biological outcome for selected cells.
Return to top

Neurochemical insights into the radiation protection of astronauts: Distinction between low- and moderate-LET radiation components
Belov OV, Belokopytova KV, Kudrin VS, Molokanov AG, Shtemberg AS, Bazyan AS. Phys Med. 2019 Jan;57:7-16. [3/19]
Radiation protection of astronauts remains an ongoing challenge in preparation of deep space exploratory missions. Exposure to space radiation consisting of multiple radiation components is associated with a significant risk of experiencing central nervous system (CNS) detriments, potentially influencing the crew operational decisions. Developing of countermeasures protecting CNS from the deleterious exposure requires understanding the mechanistic nature of cognitive impairments induced by different components of space radiation. The current study was designed to identify differences in neurochemical modifications caused by exposure to low- and moderate-LET radiations and to elucidate a distinction between the observed outcomes. We exposed rats to accelerated protons (170 MeV; 0.5 keV/μm) or to carbon ions (12C; 500 MeV/u; 10.5 keV/μm) delivered at the same dose of 1 Gy. Neurochemical alterations were evaluated 1, 30, and 90 days after exposure via indices of the monoamine metabolism measured in five brain structures, including prefrontal cortex, hypothalamus, nucleus accumbens, hippocampus and striatum. We obtained the detailed patterns of neurochemical modifications after exposure to the mentioned radiation modalities. Our data show that the enhancement in the radiation LET from relatively low to moderate values leads to different neurochemical outcomes and that a particular effect depends on the irradiated brain structure. We also hypothesized that exposure to the moderate-LET radiations can induce a hyperactivation of feedback neurochemical mechanisms, which blur metabolic deviations and lead to the delayed impairments in brain functions. Based on our findings we discuss possible contribution of the observed changes to behavioural impairments.
Return to top

Effects of High- and Low-LET Radiation on Human Hematopoietic System Reconstituted in Immunodeficient Mice.
Hoehn D, Pujol-Candell M, Young EF, Serban G, Shuryak I, Maerki J, Xu Z, Chowdhury M, Luna AM, Vlad G and Smilenov LB. Radiat Res. 191, 162–175 (2019). [3/19]
Over the last 50 years, a number of important physiological changes in humans who have traveled on spaceflights have been catalogued. Of major concern are the short- and long-term radiation-induced injuries to the hematopoietic system that may be induced by high-energy galactic cosmic rays encountered on interplanetary space missions. To collect data on the effects of space radiation on the human hematopoietic system in vivo, we used a humanized mouse model. In this study, we irradiated humanized mice with 0.4 Gy of 350 MeV/n 28Si ions, a dose that has been shown to induce tumors in tumor-prone mice and a reference dose that has a relative biological effectiveness of 1 (1 Gy of 250-kVp X rays). Cell counts, cell subset frequency and cytogenetic data were collected from bone marrow spleen and blood of irradiated and control mice at short-term (7, 30 and 60 days) and long-term (6–7 months) time points postirradiation. The data show a significant short-term effect on the human hematopoietic stem cell counts imparted by both high- and low-LET radiation exposure. The radiation effects on bone marrow, spleen and blood human cell counts and human cell subset frequency were complex but did not alter the functions of the hematopoietic system. The long-term data acquired from high-LET irradiated mice showed complete recovery of the human hematopoietic system in all hematopoietic compartments. The combined results demonstrate that, in spite of early perturbation, the longer term effects of high-LET radiation are not detrimental to human hematopoiesis in our system of study.
Return to top

Radiation and microgravity – Associated stress factors and carcinogenesis.
Moreno-Villanueva M, Wu H. REACH. 2019 Mar;13:100027. [3/19]
Defects in signaling networks that regulate cellular activities, such as growth and survival can lead to cancer development. Space environment affects signal molecules and genes involve in DNA damage response, cell proliferation, cell metabolism, and cytoskeleton signaling among others. Reduced gravity and exposure to harmful radiation are the main stress factors encountered in space. While a potential risk of tumor initiation has been extensively investigated for space-radiation, research efforts on the effects of microgravity on cancer cells have focused mainly on tumor progression and migration. However, the space environment comprises both cosmic radiation and reduced gravity, and, therefore, potential additive or synergistic effects need to be considered. For instance, impaired DNA repair processes due to lack of gravity can compromise the cellular response to radiation, which in turn leads to accumulation of DNA damage and increase of the risk of tumor initiation and progression. In this review, recent research aiming at identifying the association between space radiation, microgravity or the combination of both with tumor development and the possible underlying cellular mechanisms is summarized. Furthermore, space-associated stress factors, such as psychological stress, sleep disturbances or the potential role of the immune system in tumor initiation and development in space are discussed.
Return to top

On the decision making criteria for cis-lunar reference mission scenarios.
El-Jaby S, Lewis BJ, Tomi L. Life Sci Space Res. 2019 Feb 28. [Article in Press] [3/19]
Space agencies are currently developing reference mission scenarios to determine if occupational dose limits, already adopted for low-Earth orbit (LEO) missions to the International Space Station (ISS), are also applicable for deep space cis-lunar missions. These cis-lunar missions can potentially last upwards of a year, during which astronauts will experience a daily low-dose from galactic cosmic radiation (GCR) and a potentially high-dose from single, or multiple, solar particle events (SPEs). Unlike GCR exposure, SPEs are difficult to predict and model due to their sporadic nature. Consequently, mission planners have decided to rely on historical SPE spectra to prepare for the ‘worst case’ scenario. Assuming a spherical aluminum shell as a reference spacecraft, this paper demonstrates how the choice of SPE parametric model, shield thickness, dose metric, and radiation transport code can impact the decision-making criteria for the worst case SPE, the estimated GCR dose, and consequently whether current LEO dose limits are applicable.
Return to top

The Million Person Study, whence it came and why.
Boice JD Jr, Cohen SS, Mumma MT, Ellis ED. Int J Radiat Biol. 2019 Mar 4. [Epub ahead of print] [3/19]
The study of low dose and low-dose rate exposure is of immeasurable value in understanding the possible range of health effects from prolonged exposures to radiation. The Million Person Study of Low-Dose Health Effects (MPS) was designed to evaluate radiation risks among healthy American workers and veterans who are more representative of today's populations than are the Japanese atomic bomb survivors exposed briefly to high-dose radiation in 1945. A million persons were needed for statistical reasons to evaluate low-dose and dose-rate effects, rare cancers, intakes of radioactive elements, and differences in risks between women and men.
Return to top

The Million Person Study relevance to space exploration and Mars
Boice JD Jr. Int J Radiat Biol. 2019 Mar 4. [Epub ahead of print] [3/19]
Understanding the health consequences of exposure to radiation received gradually over time is critically needed. The National Aeronautics and Space Administration (NASA) bases its safety standards on the acute exposures received by Japanese atomic bomb survivors. Such a brief exposure differs appreciably from the chronic radiation received during a two to three year mission to Mars. NASA also applies an individual risk-based system for radiation protection that accounts for age, sex, smoking history and individual life styles. Because the Japanese life span study (LSS) reports women to be at 2 to 3 times greater lifetime risk of developing cancer than men, female astronauts are allowed less time in space. Another concern is the potential behavioral and cognitive impairments from galactic cosmic radiation (GCR) impinging on the nervous system that might jeopardize the mission, and, possibly, lead to dementia later in life. GCR are high-velocity heavy ions traveling through space. There are no human circumstances/analogs similar to GCR that can provide direct information on the possible effects of such high-LET exposure to brain tissue.
Return to top

Behavioral effects of space radiation: A comprehensive review of animal studies
Kiffer F, Boerma M, Allen A. Life Sci Space Res. 2019 Feb 19. [Article in Press] [3/7]
This article provides a comprehensive review of prior published work on the effects of protons, helium and heavy ions on cognitive function in mouse and rat models. As this field of research is currently in a transition towards studying mixed ion fields, this review is intended as a reference of prior results of behavioral assays after single ion exposures.
Return to top

Synergy theory for murine Harderian gland tumours after irradiation by mixtures of high-energy ionized atomic nuclei
Huang EG, Lin Y, Ebert M, Ham DW, Zhang CY, Sachs RK. Radiat Environ Biophys. 2019 Feb 2. doi:10.1007/s00411-018-00774-x. [Epub ahead of print] [3/4]
Experimental studies reporting murine Harderian gland tumorigenesis induced by accelerator beams of ions in the galactic cosmic ray (GCR) spectrum have been a NASA concern for many years. It is not currently known whether GCR have significant synergy. Synergy would increase the health risks of astronaut voyages in interplanetary space. This paper uses in silico synergy theory to analyze prospective GCR-simulating ion-mixture experiments. The "obvious" simple effect additivity (SEA) approach of comparing an observed mixture dose-effect relationship (DER) to the sum of the components' DERs is known from other fields of biology to be unreliable when the components' DERs are highly curvilinear, so many different replacements are now being used. Such curvilinearity may be present at low fluxes in the one-ion Harderian gland experiments due to non-targeted ('bystander') effects, in which case a replacement for SEA synergy theory is needed. This paper uses a recently introduced, arguably optimal, replacement for SEA: incremental effect additivity (IEA). It is based on numerical integration of non-linear ordinary differential equations. Unlike SEA and almost all its replacements, IEA synergy theory obeys the mixture of mixtures principle, important because even a one-ion beam on entry often becomes mixed due to interactions with intervening matter. To illustrate IEA synergy theory, prospective experiments using rapidly-sequential beams are studied with customized open-source software. Tight 95% confidence intervals are calculated taking into account adjustable parameter correlations. Arguments are presented against NASA emphasizing accelerator experiments with mixed beams whose mixture composition is standardized rather than being adjustable to take biological variability into account.
Return to top

Experimental Assessment of Lithium Hydride's Space Radiation Shielding Performance and Monte Carlo Benchmarking.
Schuy C, La Tessa C, Horst F, Rovituso M, Durante M, Giraudo M, Bocchini L, Baricco M, Castellero A, Fioreh G, Weber U. Radiation Research, 191(2):154-161 (2018). [2/20]
In the current experimental campaign, the shielding performance of lithium hydride was assessed by measuring normalized dose, primary beam attenuation and neutron ambient dose equivalent using 430 MeV/u 12C, 600 MeV/u 12C and 228 MeV proton beams. The experimental data were then compared to predictions from the Monte Carlo transport codes PHITS and GRAS. The experimental results show an increased shielding effectiveness of lithium hydride compared to reference materials like polyethylene. For instance, the attenuation length for 600 MeV/u 12C primary particles in lithium hydride is approximately 20% shorter compared to polyethylene. Furthermore, the comparison results between both transport codes indicates that the standard Tripathi-based total reaction cross-section model of PHITS cannot accurately reproduce the presented experimental data, whereas GRAS shows reasonable agreement.
Return to top

GeneLab database analyses suggest long-term impact of space radiation on the cardiovascular system by the activation of FYN through reactive oxygen species.
Beheshti A, McDonald JT, Miller J, Grabham P, Costes SV. Int J Mol Sci. 2019 Feb 3;20(3):E661. [2/19]
Three GeneLab datasets were used to provide a potentially novel mechanism for space radiation induced cardiovascular risk directly linking radiation ground studies to spaceflight. Two of the datasets encompassed simulated space radiation ground studies and one was an in vitro spaceflight study focusing on the cardiovascular system. The following novel findings emerged from this study: 1) Space radiation causes downregulation of reactive oxygen species (ROS) functions in the cardiovascular system; 2) Astronauts and samples on the ISS are experiencing more proton radiation than any other type of space radiation; and 3) From our study we hypothesize that a feedback loop occurs from the oxidative stress caused by space radiation that upregulates a key driving gene called FYN, which in turn reduces ROS levels and thus ROS pathways, preventing cell death of cardiovascular related cells and thus protecting the cardiovascular systems.
Return to top

Exposure to ≤15 cGy of 600 MeV/n 56Fe Particles Impairs Rule Acquisition but not Long-Term Memory in the Attentional Set-Shifting Assay
Jewell JS, Duncan VD, Fesshaye A, Tondin A, Macadat E, and Britten RA. Radiation Research. 190(6):565-575, 2018. [2/14]
This paper describes our study of the impact of 56Fe ions (a major component of Galactic Cosmic rays) on the ability of rats to perform attentional set shifting (ATSET), one form of executive function. In this study we used rats that were maintained on a rigorous exercise regimen and that were prescreened for competency in the ATSET test. We discovered that the rats maintained a good working memory of the rules of the ATSET test for at least 6 months, even after irradiation, but that the irradiated rats had an impaired ability to learn a new set of rules when presented with a modified version of the ATSET test. Should similar effects occur in astronauts, exposure to space radiation may only impact the astronauts' ability to solve problems that they have not previously encountered.
Return to top

Effects of head-only or whole-body exposure to very low doses of 4He (1000 MeV/n) particles on neuronal function and cognitive performance
Rabin BM, Poulose SM, Bielinski DF, Shukitt-Hale B. Life Sci Space Res. 2019 Feb 5. [Article in Press] [2/12]
A significant portion of the total dose experienced by astronauts may be expected to come from exposure to low LET 4He particles. Changes in neuronal function and cognitive performance could be observed following both head-only and whole-body exposures to 4He particles at doses as low as 0.01–0.025 cGy. These results, therefore, suggest the possibility that astronauts on exploratory class missions may be at a greater risk for HZE-induced deficits than previously anticipated.
Return to top

Psycho-emotional status but not cognition is changed under the combined effect of ionizing radiations at doses related to deep space missions
Kokhan VS, Shakhbazian EV, Markova NA. Behav Brain Res. 2019 Jan 15;362:311-8. [2/6]
Initially, the paradigm about the strictly negative impact of ionizing radiation (IR) on the central nervous system dominated. However, data on the stimulating effect of moderate doses of ionizing radiation on cognitive abilities, as well as on the anxiolytic and antidepressant effects of IR, gradually accumulated. In the present work, a study was conducted of the serotonergic system in the brain structures that are closely involved in the implementation of the response to stress. The results revealed an anxiogenic and, at the same time, antidepressant effect of IR. At the same time, the positive effect of IR on the spatial learning performance of rats was obtained. Obviously, we are seeing a number of neurocompensatory and neuroadaptive CNS reactions to the effect of IR. Within the limits of sensitivity of the tests used and within the limits of doses of the combination of ionizing radiations used (comparable to that in the implementation of the 860-day Mars mission), we conclude that IR is relatively safe for CNS functions.
Return to top

Clustered DNA double-strand break formation and the repair pathway following heavy-ion irradiation
Hagiwara Y, Oike T, Niimi A, Yamauchi M, Sato H, Limsirichaikul S, Held KD, Nakano T, and Shibata A. J Radiat Res, 2018, pp. 1–11. [2/6]
Photons, such as X- or γ-rays, induce DNA damage (distributed throughout the nucleus) as a result of low-density energy deposition. In contrast, particle irradiation with high linear energy transfer (LET) deposits high-density energy along the particle track. High-LET heavy-ion irradiation generates a greater number and more complex critical chromosomal aberrations, such as dicentrics and translocations, compared with X-ray or γ irradiation. In addition, the formation of >1000 bp deletions, which is rarely observed after X-ray irradiation, has been identified following high-LET heavy-ion irradiation. Previously, these chromosomal aberrations have been thought to be the result of misrepair of complex DNA lesions, defined as DNA damage through DNA double-strand breaks (DSBs) and single-strand breaks as well as base damage within 1-2 helical turns (<3-4 nm). In this review, we summarize the latest findings regarding the hallmarks of DNA damage structure and the repair pathway following heavy-ion irradiation. Furthermore, we discuss the mechanism through which high-LET heavy-ion irradiation may induce dicentrics, translocations and large deletions.
Return to top

Radiation-induced genomic instability, epigenetic mechanisms and the mitochondria: A dysfunctional ménage a trois?
Baulch JE. Int J Radiat Biol. 2018 Nov 19. [Epub ahead of print] [2/5]
This article presents a perspective examining the evidence for a link between radiation-induced genomic instability, epigenetic mechanisms and mitochondrial dysfunction. Significant evidence suggests that mitochondrial dysfunction accompanies radiation-induced genomic instability. Similarly, it is well recognized that mitochondria synthesize the methyl, acetyl and phosphate donors necessary for covalent DNA and histone modifications. Although we have long invoked epigenetic mechanisms as drivers of persistent genomic instability, most studies arguably provide only correlative data to support this assertion.
Return to top

Mechanistic modeling predicts no significant dose rate effect on heavy-ion carcinogenesis at dose rates relevant for space exploration
Shuryak I, Brenner DJ. Radiat Prot Dosimetry. 2018 Dec 11. [Epub ahead of print] [2/1]
Based on a mix of experimental carcinogenesis data from rodent models and epidemiological studies of uranium miners, we generated model-based quantitative estimates of dose-rate-effects, relative to acute exposures, for densely-ionizing GCR-induced lung carcinogenesis. We used a mechanistically-motivated biophysical model which includes and quantifies both targeted and non-targeted radiation effects. These dose rates effects are predicted to depend both on dose rate and fluence. At the CGR fluences/dose rates expected during a Mars mission, very small dose-rate effects were predicted, i.e. the risks estimated for prolonged exposure were similar to those for acute exposures. Heavy ion carcinogenesis estimates from moderate/high dose-rate experimental data may be applicable to doses/dose rates relevant for space exploration.
Return to top

The final frontier: Transient microglia reduction after cosmic radiation exposure mitigates cognitive impairments and modulates phagocytic activity
Rosi S. Brain Circ. 2018 Jul-Sep;4(3):109-13. Review. [1/23]
Here, we discuss the potential of transient microglia depletion after the brain irradiation to reset the altered immune system activation and eliminate any potential long-term cognitive effects. Temporary microglia depletion showed promise in preventing any deleterious cognitive impairments following exposure to elements of cosmic radiation, such as helium and high-charge nuclei. The understanding of long-term radiation-induced cognitive impairments is vital for the protection of future astronauts and equally as important for current cancer patients.
Return to top

Hibernation and Radioprotection: Gene Expression in the Liver and Testicle of Rats Irradiated under Synthetic Torpor
Tinganelli W, Hitrec T, Romani F, Simoniello P, Squarcio F, Stanzani A, Piscitiello E, Marchesano V, Luppi M, Sioli M, Helm A, Compagnone G, Morganti AG, Amici R, Negrini M, Zoccoli A, Durante M and Cerri M. Int J Mol Sci. 2019, 20, 352-364. [1/16]
Hibernation has been proposed as a tool for human space travel. In recent years, a procedure to induce a metabolic state known as “synthetic torpor” in non-hibernating mammals was successfully developed. Synthetic torpor may not only be an efficient method to spare resources and reduce psychological problems in long-term exploratory-class missions, but may also represent a countermeasure against cosmic rays. Here we show the preliminary results from an experiment in rats exposed to ionizing radiation in normothermic conditions or synthetic torpor. Animals were irradiated with 3 Gy X-rays and organs were collected 4 h after exposure. Histological analysis of liver and testicle showed a reduced toxicity in animals irradiated in torpor compared to controls irradiated at normal temperature and metabolic activity. The expression of ataxia telangiectasia mutated (ATM) in the liver was significantly downregulated in the group of animals in synthetic torpor. In the testicle, more genes involved in the DNA damage signaling were downregulated during synthetic torpor. These data show for the first time that synthetic torpor is a radioprotector in non-hibernators, similarly to natural torpor in hibernating animals. Synthetic torpor can be an elective strategy to protect humans during long term space exploration of the solar system.
Return to top

Francis A. Cucinotta, Murat Alp, and Eliedonna Cacao. Radiation Protection Dosimetry (2018), pp. 1–6. [12/20]
Neuron cells consist of the soma or cell body, axons, dendritic arbor with multiple branches, and dendritic spines which are the substrates for memory storage and synaptic transmission. Detriments in neuron morphology are suggested to play a key role in cognitive impairments following brain irradiation. Multiple molecular mechanisms are involved in the regulation and stability of neuron morphology, while the effects of radiation on these processes have not been studied extensively. In this report, we consider possible biological targets in neurons for energy deposition (ED) by charged particles that could lead to neuron morphology detriments, and the resulting dose and radiation quality dependence of such detriments. The track structures of heavy ions including high charge and energy (HZE) particles consists of core of high-ED events and a penumbra of sparse ED from δ-ray electrons produced in ionization of target molecules. We consider the role of track structure relative to possible targets causative in the degradation of morphology.
Return to top

Pion-heavy ion scattering total and inelastic cross sections for space radiation applications
Francis A. Cucinotta, Myung-Hee Y. Kim, Premkumar B. Saganti. Nuclear Inst. and Methods in Physics Research B 438 (2019) 14–19. [12/20]
Secondary pions are produced by cosmic ray proton and heavy ion induced collisions with spacecraft shielding materials and tissue. In this paper we describe methods for compiling a data-base of energy dependent pion-heavy ion inelastic sections for interactions of pions with common shielding and tissue atoms over a wide energy range (20 MeV to 100 GeV). We report on extensive comparisons to experimental data for energy dependent total and absorption (inelastic) cross sections. General agreement between model and experiments within 20% is found.
Return to top

Modeling Reveals the Dependence of Hippocampal Neurogenesis Radiosensitivity on Age and Strain of Rats.
Cacao E, Kapukotuwa S and Cucinotta FA. Front. Neurosci. 12:980 [12/20]
Cognitive dysfunction following radiation treatment for brain cancers in both children and adults have been correlated to impairment of neurogenesis in the hippocampal dentate gyrus. In this paper, we have extended our previous mathematical model of radiation-induced hippocampal neurogenesis impairment of C57BL/6 mice to delineate the time, age, and dose dependent alterations in neurogenesis of a diverse strain of rats. We considered four compartments to model hippocampal neurogenesis and its impairment following radiation exposures: (1) neural stem cells (NSCs), (2) neuronal progenitor cells or neuroblasts (NB), (3) immature neurons (ImN), and (4) glioblasts (GB). Additional consideration of dose and time after irradiation dependence of microglial activation and a possible shift of NSC proliferation from neurogenesis to gliogenesis at higher doses is established. A major result of this work is predictions of the rat strain and age dependent differences in radiation sensitivity and sub-lethal damage repair that can be used for predictions for arbitrary dose and dose-fractionation schedules.
Return to top

Non-Targeted Effects Lead To A Paridigm Shift In Risk Assessment For A Mission To The Earth’s Moon Or Martian Moon Phobos
Francis A. Cucinotta, Eliedonna Cacao, Myung-Hee Y. Kim and Premkumar B. Saganti. Radiation Protection Dosimetry (2018), pp. 1–6. [12/20]
Many studies suggest non-targeted effects (NTEs) occur for low doses of high-linear energy transfer (LET) radiation, leading to deviation from the linear dose response model used in radiation protection. We investigate corrections to quality factors (QF) for NTEs, which are used in predictions of fatal cancer risks for exploration missions. Prediction of fatal cancer risks for missions to the Martian moon, Phobos of 500-d and the Earth’s moon of 365-d for average solar minimum condition show increases of 2- to 4-fold higher in the NTE model compared with the conventional model. Limitations in estimating uncertainties in NTE model parameters due to sparse radiobiology data at low doses are discussed.
Return to top

Evaluation of statistical modeling approaches for epidemiologic studies of low dose radiation health effects.
Golden AP, Cohen SS, Chen H, Ellis ED, Boice JD Jr. Int J Radiat Biol. 2018 Nov 30. [Epub ahead of print] [12/19]
Evaluation of statistical modeling approaches for epidemiologic studies of low dose radiation health effects. (link to Golden AP, Cohen SS, Chen H, Ellis ED, Boice JD Jr. Int J Radiat Biol. 2018 Nov 30. [Epub ahead of print] [12/19] Summary: This study compares radiation risk estimates for leukemia other than chronic lymphocytic leukemia (non-CLL) and ischemic heart disease (IHD) produced by both Cox and Poisson regression models for time-dependent dose-response analyses of occupational exposure. The results from one cohort, the Nuclear Power Plant workers (NPP) are presented, although the evaluation considered five cohorts of varying size and exposure as part of the Million Worker Study. Cox Proportional Hazards models, with age as the underlying timescale for hazard, were conducted using three computer software programs: SAS, R, and Epicure. Doses lagged 2 years for non-CLL and 10 years for ischemic heart disease were treated as time-dependent exposures at the annual level and were examined both in categories and as a continuous term. Hazard ratios (HR) and 95% confidence intervals (CI) were reported for each model in SAS and R, while the Peanuts program of Epicure was utilized to produce Excess Relative Risk (ERR) estimates and 95% CI. All models were adjusted for gender and year of birth. Four piece-wise exponential Poisson models (log-linear regression for rate) were developed with varying cutpoints for age strata from very fine to broad categories using both R and the Amfit program in Epicure for ERR estimates. Comparable estimates of risk (both RR and ERR) were observed from Cox and Poisson models, regardless of software utilized, as long as appropriately narrow categories of age were utilized to control the confounding of age in Poisson models. The ERR estimates produced in Epicure tended to agree very closely with the HR or RR estimates, and the statistical software program used had no impact to risk estimates for the same model. The results of this evaluation support the use of the Cox proportional hazards or the ungrouped Poisson approach to analyzing time-dependent dose-response relationships to ensure that maximum control over the confounding of age is achieved in studies of mortality for cohorts occupationally exposed to radiation.
Return to top

Accelerator-Based Tests of Shielding Effectiveness of Different Materials and Multilayers using High-Energy Light and Heavy Ions.
Martina Giraudo, Christoph Schuy, Uli Weber, Marta Rovituso, Giovanni Santin, John W. Norbury, Emanuele Tracino, Alessandra Menicucci, Luca Bocchini, Cesare Lobascio, Marco Durante, and Chiara La Tessa Radiation Research 2018 190 (5), 526-537 [12/4]
Short- and long-term effects caused by exposure to cosmic radiation are among the main health risks of space travel. One of the current strategies is to find multifunctional materials that combine excellent mechanical properties with a high shielding effectiveness to minimize the overall load. In this work, the shielding effectiveness of a wide variety of single and multilayer materials of interest for different mission scenarios has been characterized. The results are presented in terms of Bragg curves and dose reduction per unit area density. To isolate the shielding effectiveness only due to nuclear fragmentation, a correction for the energy loss in the material is also considered. The output of this investigation represents a useful database for benchmarking Monte Carlo and deterministic transport codes used for space radiation transport calculations.
Return to top

Genetic variation and radiation quality impact cancer promoting cellular phenotypes in response to HZE exposure.
Sridharan DM, Enerio S, Wang C, LaBarge MA, Stampfer MR, Pluth JM. Life Sci Space Res. 2018 Oct 21. [11/12]
There exists a wide degree of genetic variation within the normal human population which includes disease free individuals with heterozygote defects in major DNA repair genes. A lack of understanding of how this genetic variation impacts cellular phenotypes that inform cancer risk post heavy ion exposure poses a major limitation in developing personalized cancer risk assessment of astronauts. We initiated a pilot study with Human Mammary Epithelial Cell strains (HMEC) and various genetic variants that were heterozygote for DNA repair genes; BRCA1, BRCA2 and ATM. The centrosome aberration frequency increases with dose, complexity of the lesion generated by different radiation qualities and age of the individual. This increase in genomic instability correlates with elevated check-point activation post radiation exposure. These results will have significant implications in estimating cancer susceptibility in genetically variant individuals exposed to HZE particles.
Return to top

Space radiation triggers persistent stress response, increases senescent signaling, and decreases cell migration in mouse intestine
Kumar S, Suman S, Fornace AJ Jr, Datta K., published in Proc Natl Acad Sci U S A. 2018 Oct 1. [Epub ahead of print] [10/10]
Kumar et al. report that HZE ion radiation leads to important long-term perturbations in intestinal function. The Georgetown group showed ten years ago that HZE ions induce a persistent oxidative-stress state and pro-inflammatory phenotype in gastrointestinal (GI) and other tissues. The Shay laboratory (a member of their GI NSCOR program) further expanded on this in a 2015 report in Oncogene showing changes in gene expression in GI tissues reminiscent of the senescence-associated inflammatory response (SIR) after space radiation. In the current publication, the authors now show that HZE ions trigger perturbations in key proteins and often their transcript levels that are known to control normal GI epithelial cell maturation and function. Interestingly, cell migration along the crypt-villus axis in small intestine was persistently decreased after a low dose of 56Fe radiation relative to control and γ-rays. Wnt/β-catenin and its downstream EphrinB/EphB signaling are key to GI epithelial proliferation and positioning during migration, and both were upregulated. In addition, factors involved in cell polarity, cell adhesion, and cell-extracellular matrix interactions were persistently downregulated. These changes were accompanied by changes in barrier function and nutrient absorption factors, as well as increased intestinal tumorigenesis. Along with these changes, increasing levels of oxidative stress and DNA damage were seen up to a year after irradiation. These effects correlated with higher levels of senescent cells in GI crypts and features of the senescence-associated secretory phenotype (SASP) and the SIR. A working model was proposed whereby HZE ions cause sufficient damage to induce senescent GI cells, and that senescent-cell associated signaling molecules trigger long-term oxidative stress and a feedback loop leading to a gradual increase in senescent cells in GI crypts with increasing levels of DNA damage.
Return to top

Should NASA collect astronauts’ genetic information for occupational surveillance and research?
Reed RD, Antonsen EL. AMA J Ethics. 2018 Sep 1;20(9):E849-56. [10/9]
Humans exploring beyond low-Earth orbit face environmental challenges coupled with isolation, remote operations, and extreme resource limitations in which personalized medicine, enabled by genetic research, might be necessary for mission success. With little opportunity to test personalized countermeasures broadly, the National Aeronautics and Space Administration (NASA) will likely need to rely instead on collection of significant amounts of genomic and environmental exposure data from individuals. This need appears at first to be in conflict with the statutes and regulations governing the collection and use of genetic data. In fact, under certain conditions, the Genetic Information Nondiscrimination Act (GINA) of 2008 allows for the use of genetic information in both occupational surveillance and research and in the development of countermeasures such as personalized pharmaceuticals.
Return to top

Proton radiation-induced cancer progression
Luitel K, Bozeman RG, Kaisani A, Kim SB, Barron S, Richardson JA, Shay JW. Life Sci Space Res. 2018 Aug 18. [9/11]
In this study, the long-term side effects of proton radiation are compared to equivalent doses of X-rays in the initiation and progression of premalignant lesions in a lung cancer susceptible mouse model (K-rasLA1). Exposure to proton irradiation enhances the progression of premalignant lesions to invasive carcinomas through persistent DNA damage, chronic oxidative stress, and immunosuppression.
Return to top

Temporary microglia-depletion after cosmic radiation modifies phagocytic activity and prevents cognitive deficits.
Krukowski K, Feng X, Paladini MS, Chou A, Sacramento K, Grue K, …, Rosi S. Scientific Reports, 8, 7857 (2018). [8/31]
Temporary microglia depletion, one week after cosmic radiation, prevents the development of long-term memory deficits. The repopulated microglia present a modified functional phenotype with reduced phagocytic activity shown to be involved in microglia-synapses interaction. Our data provide mechanistic evidence for the role of microglia in the development of cognitive deficits after cosmic radiation exposure. To our knowledge this is the first report to identify a therapeutic approach for treating GCR-induced deficits.
Return to top

Female mice are protected from space radiation-induced maladaptive responses
Krukowski K, Grue K, Frias ES, Pietrykowski J, Jones T, Nelson G, Rosi S. Brain Behav Immun. 2018 Aug 11. [8/28]
A single exposure to simulated GCR induces long-term cognitive and behavioral deficits only in the male cohorts but not in female. Mechanistically, the maladaptive behavioral responses observed only in the male cohorts correspond with microglia activation and synaptic loss in the hippocampus, a brain region involved in the cognitive domains reported here. Our findings suggest that GCR exposure can regulate microglia activity and alter synaptic architecture, which in turn leads to a range of cognitive alterations in a sex dependent manner.
Return to top

Exposure to galactic cosmic radiation compromises DNA repair and increases the potential for oncogenic chromosomal rearrangement in bronchial epithelial cells.
Li Z, Jella KK, Jaafar L, Li S, Park S, Story MD, Wang H, Wang Y, Dynan WS. Sci Rep. 2018 Jul 23;8(1):11038. (8/21)
The authors of this study investigated persistent effects of galactic cosmic ray exposure on DNA repair capacity in human lung-derived epithelial cells, Replicate cell cultures were irradiated with 48-Ti ions or reference γ-rays, then challenged by expression of a Cas9/sgRNA pair that creates double-strand breaks simultaneously in the EML4 and ALK loci. Misjoining, which creates an EML4-ALK fusion oncogene, was significantly elevated in 48-Ti-irradiated populations relative to controls or γ-ray-irradiated samples and was frequently accompanied by deletions, consistent with a shift toward error-prone alternative nonhomologous end joining repair.
Return to top

Cancer and circulatory disease risks for a human mission to Mars: Private mission considerations.
Cucinotta FA, Cacao E, Kim M-HY, Saganti PB. Acta Astronaut. 2018 Aug 13. (8/18)
There is growing interest in private missions to Mars and other deep space destinations within the next decade. Private missions could consider persons not restricted by radiation limits; however there remains an interest in the level of risk to be encountered. Astronauts and cosmonauts are typically above 40-y, while younger aged persons could participate in private space missions. This paper describes cancer and circulatory disease risks for a 940 d Mars mission for average solar minimum conditions for persons of varying ages from 20 to 60 years. For the first-time NTEs are considered in Mars mission cancer risk predictions. We find much higher importance of cancer risk compared to circulatory disease risks for persons participating in space missions.
Return to top

Charged-Iron-Particles Found in Galactic Cosmic Rays are Potent Inducers of Epithelial Ovarian Tumors.
Mishra B, Lawson GW, Ripperdan R, Ortiz L, Ludere U. Radiation Research 190(2):142-150. 2018. (8/18)
Astronauts traveling in deep space are exposed to radioactive particles, such as iron ions, from galactic cosmic rays. We previously showed that irradiation of adult female mice with iron ions destroys ovarian follicles, causing premature ovarian failure, and we hypothesized that these mice would subsequently develop ovarian tumors. To test this, we aged female mice for 15 months after irradiation with 50 cGy iron ions, which is about the total dose of radiation astronauts would receive during a 3 year Mars mission. Irradiated mice had a 4-fold increased incidence of ovarian tumors compared to non-irradiated controls. The tumors were positive for cytokeratin, indicating that they were epithelial tumors. Most human ovarian cancers are also epithelial. These results raise concerns about ovarian tumors as possible late consequences of deep space travel in female astronauts.
Return to top

Comparative profiling of microRNAs reveals the underlying toxicological mechanism in mice testis following carbon ion radiation.
He Y, Zhang Y, Li H, Zhang H, Li Z, Xiao L, Hu J, Ma Y, Zhang Q, Zhao X. Dose Response. 2018 Apr-Jun;16(2):1559325818778633. (8/16)
This study investigated the toxicity of heavy ion radiation to mice testis by microRNA (miRNA) sequencing and bioinformatics analyses. Testicular indices and histology were measured following enterocoelia irradiation with a 2 Gy carbon ion beam, with the testes exhibiting the most serious injuries at 4 weeks after carbon ion radiation (CIR) exposure. Illumina sequencing technology was used to sequence small RNA libraries of the control and irradiated groups at 4 weeks after CIR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses implicated differential miRNAs in the regulation of target genes involved in metabolism, development, and reproduction. Here, 8 miRNAs, including miR-34c-5p, miR-138, and 6 let-7 miRNA family members previously reported in testis after radiation, were analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) to validate miRNA sequencing data. The differentially expressed miRNAs described here provided a novel perspective for the role of miRNAs in testis toxicity following CIR.
Return to top

Biodosimetric transcriptional and proteomic changes are conserved in irradiated human tissue.
Keam, S.P., Gulati, T., Gamell, C. et al. Radiat Environ Biophys (2018) 57: 241. (8/16)
Transcriptional dosimetry is an emergent field of radiobiology aimed at developing robust methods for detecting and quantifying absorbed doses using radiation-induced fluctuations in gene expression. A combination of RNA sequencing, array-based and quantitative PCR transcriptomics in cellular, murine and various ex vivo human models has led to a comprehensive description of a fundamental set of genes with demonstrable dosimetric qualities. However, these are yet to be validated in human tissue due to the scarcity of in situ-irradiated source material. In this study, we present a novel evaluation of a previously reported set of dosimetric genes in human tissue exposed to a large therapeutic dose of radiation. To do this, we evaluated the quantitative changes of a set of dosimetric transcripts consisting of FDXR, BAX, BCL2, CDKN1A, DDB2, BBC3, GADD45A, GDF15, MDM2, SERPINE1, TNFRSF10B, PLK3, SESN2 and VWCE in guided pre- and post-radiation (2 weeks) prostate cancer biopsies from seven patients. We confirmed the prolonged dose-responsivity of most of these transcripts in in situ-irradiated tissue. BCL2, GDF15, and to some extent TNFRSF10B, were markedly unreliable single markers of radiation exposure. Nevertheless, as a full set, these genes reliably segregated non-irradiated and irradiated tissues and predicted radiation absorption on a patient-specific basis.
Return to top

Comparing HZETRN, SHIELD, FLUKA and GEANT transport codes.
John W. Norbury, Tony C. Slaba, Nikolai Sobolevsky, Brandon Reddell. NASALife Sciences in Space Research 14 (2017) 64–73. (7/16)
This paper represents the first direct comparisons of the American (NASA) and Russian (ROSCOSMOS) space radiation transport codes, HZETRN and SHIELD. Flux spectra of neutrons, light ions, heavy ions and pions were calculated for galactic cosmic ray projectiles incident on Aluminum. Some comparison calculations with the GEANT4 and FLUKA transport codes were also shown. Overall, the biggest differences between transport codes occur below the several hundred MeV region, which may be due to the differences in nuclear models employed in the different codes.
Return to top

SHIELD and HZETRN comparisons of pion production cross sections.
John W. Norburya, Nikolai Sobolevsky, Charles M. Werneth. Nuclear Inst, and Methods in Physics Research B 418 (2018) 13–17. (7/16)
The present work represents the second time that NASA and ROSCOSMOS calculations have been directly compared, and the focus here is on models of pion production cross sections used in the HZETRN (NASA) and SHIELD (ROSCOSMOS) transport codes. It was found that these models are in moderate agreement with each other and with experimental data, and further model improvements would be worthwhile.
Return to top

Comparison of space radiation GCR models to recent AMS data.
John W. Norbury, Kathryn Whitman, Kerry Lee, Tony C. Slaba, Francis F. Badavi. Life Sciences in Space Research 18 (2018) 64–71. (7/16)
This paper is the third in a series of comparisons of American (NASA) and Russian (ROSCOSMOS) space radiation calculations. The present work focuses on calculation of fluxes of galactic cosmic rays (GCR), which are a constant source of radiation that constitutes one of the major hazards during deep space exploration missions for both astronauts/cosmonauts and hardware. In this work, commonly used GCR models are compared with recently published measurements of cosmic ray Hydrogen, Helium, and the Boron-to-Carbon ratio from the Alpha Magnetic Spectrometer (AMS). All of the models were developed and calibrated prior to the publication of the AMS data; therefore this an opportunity to validate the models against an independent data set. Overall, the different GCR models are in good agreement with AMS data in energy regions important for space radiation.
Return to top

Older In the News items may be found in the Bibliography or in the THREE Archive.


Basic Concepts of Space Radiation

In order to understand the space radiation risks faced by human explorers, it is necessary to have a clear idea of what it is, where it is, and what happens when space radiation interacts with matter. The articles in this section describe the space radiation environment, the nuclear and atomic interactions with the constituent atoms of materials – especially living materials – in space, and the ways in which energy is deposited in biologically significant molecules.

Some of the articles are taken from the Appendices of a 1998 Strategic Plan I authored during my tenure at NASA and others are presentations given by NASA Summer School faculty. There is a fair amount of overlap, both within this section and between this section and other sections, where the subjects are discussed in greater detail. This is welcome, reflecting as it does, different – and broadening – perspectives on the topics covered.

Walter Schimmerling
THREE Chief Editor

  • The Space Radiation Environment
    • Introduction – Walter Schimmerling (Article)
    • The Natural space Ionizing Radiation Environment – Patrick O’Neill (Article)
    • Fluence Rates, Delta Rays and Cell Nucleus Hit Rates from Galactic Cosmic Rays – Stanley B Curtis (PDF)
    • Solar Particle Events and Radiation Exposure in Space – Shaowen Hu (PDF)
  • Interactions of Radiation with Matter – Walter Schimmerling (Article)
    • Particle Interactions Overview – Lawrence Heilbronn (swf)
    • Physics Summary – Lawrence Heilbronn (swf)
    • Neutron Properties and Definitions – Lawrence Heilbronn (swf)
    • Neutron Lectures Supplement – Lawrence Heilbronn (PDF)
  • Dose and Dose Rate Effectiveness Factors – Walter Schimmerling  (Article)
    • Low LET Physics Topics – Gregory Nelson (swf)  Introduction (PDF)
    • A Note On The Dose-Rate-Effectiveness Factor and its Progeny 
      DDREF -  R.J.M. Fry (PDF)
  • Track Structure
    • Introduction to Track Structure and z*22 - Stanley B. Curtis (PDF)
    • Radiation Quality and Space Radiation Risks – Francis Cucinotta (swf)
    • Development of Monte Carlo Track Structure Codes – Larry Toburen (PDF)
    • Microdosimetry and Detector Responses – Leslie A. Braby (PDF)
    • Interpreting Microdosimetric Spectra – J. F. Dicello and F. A Cucinotta (PDF)
    • Monte Carlo Track Simulations – Michael Dingfelder (PDF)
    • Radiation Track Structure – Dudley T. Goodhead (swf) Abstract (PDF)
  • Elementary Concepts of Shielding – Walter Schimmerling  (PDF)
    • Heavy Ions and Shielding Physics – Lawrence Heilbronn (swf)


Introduction to THREE
Walter Schimmerling

Video presentation of
Research Solutions to Space Radiation Impacts on Human Exploration
Slides in PDF format
Francis A. Cucinotta, Ph.D.
Chief Scientist, Space Radiation Program
NASA Johnson Space Center
Houston, Texas
Aerospace Medicine Grand Rounds
March 23, 2010

Radiation and Human Space Exploration Video
NASA Human Research Program

Radiation tracks and radiation track simulation video
Ianik Plante, Ph.D.
Universities Space Research Association
Division of Space Life Sciences
NASA Johnson Space Center
Houston, Texas

Radiation tracks and radiation track simulation video is excerpted from the article:
Radiation chemistry and oxidative stress (PDF)
Ianik Plante, Ph.D.

Video Presentation of
Space Radiation and Cataracts
Eleanor Blakely
Life Sciences, Lawrence Berkeley National Laboratory
Berkeley, California
July 16, 2003


Glossary derived from:
Human Research Program Integrated Research Plan, Revision A, (January 2009). National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas 77058, pages 232-280.

Exploration Systems Radiation Monitoring Requirements (Sept 2012). Page ii. Ronald Turner.

Report No. 153: Information Needed to Make Radiation Protection Recommendations for Space Missions Beyond Low-Earth Orbit (2006). National Council on Radiation Protection and Measurements, pages 309-318.  Reprinted with permission of the National Council on Radiation Protection and Measurements.

Managing Space Radiation Risk in the New Era of Space Exploration (2008). Committee on the Evaluation of Radiation Shielding for Space Exploration, National Research Council. National Academies Press, pages 111-118.

Contents: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Printer-Friendly PDF


AAPM: American Association of Physicists in Medicine.

absolute risk: Expression of excess risk due to exposure as the arithmetic difference between the risk among those exposed and that obtaining in the absence of exposure.

absorbed dose (D): Average amount of energy imparted by ionizing particles to a unit mass of irradiated material in a volume sufficiently small to disregard variations in the radiation field but sufficiently large to average over statistical fluctuations in energy deposition, and where energy imparted is the difference between energy entering the volume and energy leaving the volume. The same dose has different consequences depending on the type of radiation delivered. Unit: gray (Gy), equivalent to 1 J/kg.

ACE: Advanced Composition Explorer Mission, launched in 1997 and orbiting the L1 libration point to sample energetic particles arriving from the Sun and interstellar and galactic sources.  It also provides continuous coverage of solar wind parameters and solar energetic particle intensities (space weather).  When reporting space weather, it can provide an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts.

acute effects: short-term biological effects of exposure to radiation, including headaches, dizziness, nausea, and illness that can range from mild to fatal.

acute exposure: Radiation exposure of short duration.

AGS: Alternating Gradient Synchrotron (at Brookhaven National Laboratory).

ALARA (As Low As Reasonably Achievable):  An essential operational safety requirement, as well as a regulatory requirement, that em­phasizes keeping exposure to radiation as low as possible using reasonable methods, and not treating dose limits as “tolerance values”; defined at NASA as limiting radiation exposure to a level that will result in an estimated risk below the limit of the 95 percent confidence level.

albedo: secondary radiation produced by interactions of galactic cosmic rays and high-energy solar protons with matter in the atmosphere or on the surface.

ALL: acute lymphocytic leukemia.

alpha particle: An energetic charged nucleus consisting of two protons and two neutrons. This particle is identical to the 4He nucleus.

ALTEA: Anomalous Long-Term Effects in Astronauts study .

AM: amplitude modulation.

AMA: American Medical Association.

AMAC: American Medical Advisory Committee.

AML: acute myelogenous leukemia.

Amu: atomic mass unit (ALSO: u).

ANLL: acute nonlymphocytic leukemia.

annual risk: The risk in a given year from an earlier exposure. The annual risk (average) from an exposure is the lifetime risk divided by the number of years of expression.

ANP: atrial natriuretic peptide.

ANS: American Nuclear Society.

ANSI: American National Standards Institute.

AU: Astronomical Unit (distance from the Earth to the Sun)

Apoe4: Apoliprotein E isoform 4. Modification of Apo4 is major risk factor in Alzheimer's disease.

apoptosis: A specific mode of cell death (also known as programmed cell death) that can be triggered by exposure to radiation, especially in cells of lymphoid/myeloid or epithelial lineage. Extensive apoptosis contributes to the hematopoietic and gastrointestinal symptoms seen in acute radiation syndrome.

ARC: NASA Ames Research Center.

Ares V/Heavy Lift Launch Vehicle: a NASA vehicle intended to deliver cargo from Earth to low Earth orbit.

ARM: Atmospheric Radiation Measurements.

ascent stage: The pressurized upper stage of the Lunar Lander in which the crew pilots the lander from lunar orbit to the lunar surface and return. The ascent stage takes off from the descent stage, leaving the latter behind on the surface.

AT: ataxia telangiectasia.

ATM: ataxia telangiectasia mutated.

AU: Astronomical Unit (Approx. distance from the Earth to the Sun)

AX-2: NASA Ames Research Center Experimental Suit 2, designed during the Apollo program as a lunar surface hard suit to bend at the waist and rotate in the torso so that the crew member can reach down to the ground with one hand. Fabricated from fiberglass.

AX-5: NASA Ames Research Center Experimental Suit 5, designed during the Space Station Advanced Development program to provide a durable hard suit for extended operations in zero gravity. Fabricated from numerically milled aluminum forgings.

Back to top


background radiation: The amount of radiation to which a member of the population is exposed from natural sources, such as terrestrial radiation from naturally-occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally-occurring radionuclides deposited in the human body. The natural background radiation received by an individual depends on geographic location and living habits. In the United States, the background radiation is on the order of 1 mSv y–1, excluding indoor radon which amounts to ~2 mSv/year on average.

BAF: Booster Applications Facility (the name used to designate the NSRL during planning and construction phases).

BaRyoN: Quark bound state with zero strangeness.

BCC: basal cell carcinoma.

BCD: budget change directive.

BEIR: Biological Effects of Ionizing Radiation. One of a series of reports on the health risks from exposure to low levels of ionizing radiation issued by the Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, Board on Radiation Effects, Research Division on Earth and Life Studies, National Research Council of the National Academies of Science of the United States, referred to by a Roman number denoting its position in the sequence of reports. At the time of this writing, the latest report is BEIR VII.

BEVALAC: An accelerator system at Lawrence Berkeley National Laboratory consisting of the Bevatron (an early, high-energy synchrotron accelerator constructed in the 1950s and used to discover the antiproton), accelerating particles delivered by the SuperHILAC (first built as the HILAC - Heavy Ion Linear Accelerator - in 1957; along with a similar one at Yale University, the first machine in the US built specifically to accelerate heavy ions, completely rebuilt into the SuperHILAC in 1971). Closed in 1993.

biological end point: effect or response being assessed, e.g., cancer, cataracts.

bipolar device: a type of semiconductor whose operation is based on both majority and minority carriers.

BNL: Brookhaven National Laboratory in Upton (Long Island), New York.

BRCA1: breast cancer 1 tumor suppressor gene.

BRCA2: breast cancer 2 tumor suppressor gene.

BrdU: bromodeoxyuridine.

BRYNTRN: BaRYoN TRaNsport code, a computer code for simulating baryon transport.

Back to top


CAD: computer aided design.

CaLV: Cargo Launch Vehicle.

CAM : computerized anatomical man model.

carbon composite: a composite incorporating carbon and other materials for use in lightweight structures, strong enough to substitute for aluminum and other metals in the construction of many parts of a spacecraft, notably the pressure vessel shell. It may incorporate boron, epoxy, polyethylene, hydrogen, or other materials that enhance radiation shielding properties.

CARD: Constellation Architecture Requirements Document; CxP 7000

cargo habitat: a crew habitat that the Lunar Lander carries for delivery to the Lunar Outpost as a key part of the “Outpost-first” strategy considered by NASA as part of the Space Exploration Initiative program.

CB: Control Board.

CDC: Center for Disease Control and Prevention.

CEDE: committed effective dose equivalent.

CENELEC: European Committee for Electrotechnical Standardization.

CEQATR: Constellation Program Environmental Qualification and Acceptance Testing Requirements; CxP 70036

CERN: European Organization for Nuclear Research.

CEV: Crew Exploration Vehicle.

CFR: Code of Federal Regulations.

CHMO: Chief Health And Medical Officer (NASA).

chronic effects: long-lasting effects of exposure to radiation; includes cancer, cataracts, and nervous system damage.

chronic exposure: Radiation exposure over long times (continuous or fractionated).

CI: confidence interval.

CL: confidence level.

CLV: Crew Launch Vehicle.

CME: coronal mass ejection, an explosion of plasma released from the atmosphere (or corona) of the Sun.

CML: chronic myelogenous leukemia.

CNP: cyclic nucleotide phosphatase.

CNS: central nervous system.

Composites: materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or microscopic scale within the finished structure.

computerized anatomical male/female: a model of human geometry used to evaluate radiation doses at various points inside the body.

Constellation system: the complete ensemble of launch vehicles, flight vehicles, ground support, support services, and lunar and planetary surface systems associated with the Vision for Space Exploration initiated during the Bush administration.

coronal mass ejection (CME): A transient outflow of plasma from or through the solar corona which may be associated with the generation of solar-particle events.

cosmic-ray modulation: The variation of the observed cosmic-ray intensity as a function of the solar cycle. The cosmic-ray intensity within the solar system is observed to vary approximately inversely with the solar activity cycle that controls the interplanetary magnetic field.

COTS: commercial, off-the-shelf.

CPD: crew passive dosimeter.

CPU: central processor unit.

CRaTER: Cosmic Ray Telescope for the Effects of Radiation.

CRCPD: Conference of Radiation Control Program Directors.

CREME96: Cosmic Ray Effects on Micro-Electronics (1996 revision), a computer code.

cross section (σ): probability per unit particle fluence of a given end point. Unit: cm2.

CT: computed tomography.

CTA: conditioned taste aversion.

CVD: cardiovascular disease.

CW: continuous wave.

CxP: Constellation Program.

Back to top


Dr: dose-rate (Gy/hr).

DAAC: Distributed Active Archive Center.

DDREF: dose and dose-rate effectiveness factor (the degree to which both dose and dose rate may influence the biological effects of exposure to a given dose of radiation).

delta rays: Electrons directly ejected from atoms in matter by radiation.

descent stage: The lower stage of the Lunar Lander that includes the descent and landing engines and propellant tanks to serve them. The crew ascending back to lunar orbit in the ascent stage leaves the descent stage behind on the lunar surface.

descent stage habitat: in the descent stage, a pressurized crew habitat in which the crew would live during sortie missions.

deterministic process: process whereby a given event will occur whenever its dose threshold is exceeded.

deterministic effects: early radiation effects usually related to a significant fraction of cell loss, exceeding the threshold for impairment of function in a tissue; so called because the statistical fluctuations in the number of affected cells are very small compared to the number of cells required to reach the threshold (ICRP 1991), above which the severity varies with dose.

detriment: Health detriment is the sum of the probabilities of all the components of health effects. These include in addition to fatal cancer the probability of heritable effects and the probability of morbidity from nonfatal cancer.

DHS: Department of Homeland Security.

DNA: deoxyribonucleic acid.

DOD: Department of Defense.

DOE: Department of Energy.

dose: A general term used when the context is not specific to a particular dose quantity. When the context is specific, the name or symbol for the quantity is used [i.e., absorbed dose (D), mean absorbed dose (DT), dose equivalent (H), effective dose (E), equivalent dose (HT), or organ dose equivalent].

dose equivalent ( H ): Estimate of radiation risk that accounts for differences in the biological effectiveness of different types of charged particles that produce the absorbed dose. H=Q × D, where Q is a quality factor based on the type of radiation (Q = 1 for x-rays). NASA uses Q as specified in ICRP Publication 60 (ICRP, 1991). Unit: sievert (Sv), equivalent to 1 J/kg.

dose limit: A limit on radiation dose that is applied by restricting exposure to individuals or groups of individuals in order to prevent the occurrence of radiation-induced deterministic effects or to limit the probability of radiation related stochastic effects to an acceptable level. For astronauts working in low-Earth orbit, unique dose limits for deterministic and stochastic effects have been recommended by NCRP.

dose rate: Dose delivered per unit time. Can refer to any dose quantity (e.g., absorbed dose, dose equivalent).

dose-response model: A mathematical formulation of the way in which the effect, or response, depends on dose.

dosimeter: A radiation detection device worn or carried by an individual to monitor the individual's radiation exposure. For space activities, a device worn or carried by an astronaut in-flight.

DREF: dose rate effectiveness factor (the degree to which dose rate may influence the biological effects of exposure to a given dose of radiation).

DRM: Design Reference Mission.

DSB: double strand break.

DSNE: Constellation Program Design Specification for Natural Environments; CxP 70023

DTRA: Defense Threat Reduction Agency.

Back to top


E: effective dose/ energy.

EAR:excess additive risk (cf. absolute risk).

ED50: dose to cause 50 % of the population to have the effect (e.g., nausea).

EDS: Earth departure stage.

EEG: electroencephalogram.

effective dose ( E ): The sum over specified tissues of the products of the equivalent dose in a tissue (HT) and the tissue weighting factor for that tissue or organ (wT) (i.e., E = wTHT). Effective dose (E) applies only to stochastic effects. Unit: sievert (Sv), equivalent to 1 J/kg.

electron volt (eV): a unit of energy equivalent to 1.602 × 10–19 joules.

ELF: extremely low frequency.

ELR: excess lifetime risk.

EMF: electromagnetic field.

EML: Environmental Measurements Laboratory, New York, NY.

EMS: emergency medical services.

EMU: Extravehicular mobility unit, the space suit developed for space shuttle crews that also serves on the ISS.  The EMU features a hard upper torso and soft lower torso, arms, and legs over the pressure bladder. The entire EMU except the helmets and boots is covered by the thermal micrometeoroid garment.

electron volt (eV): A unit of energy = 1.6 x 10–12 ergs = 1.6 x 10–19 J; 1 eV is equivalent to the energy gained by an electron in passing through a potential difference of 1 V; 1 keV = 1,000 eV; 1 MeV = 1,000,000 eV.

EOS: Earth Observing System.

EPA: Environmental Protection Agency.

equivalent dose ( HT): The product of the mean absorbed dose in an organ or tissue and the radiation weighting factor (wR) of the radiation type of interest. For external exposure wR applies to the radiation type incident on the body.

ERR:excess relative risk.

erythema: A redness of the skin.

ESA: European Space Agency.

ESMD: Exploration Systems Mission Directorate (NASA).

ESP: energetic storm particle.

ESTEC: European Space Research and Technology Centre.

EVCPDS: Extra Vehicle Charged Particle Directional Spectrometer

excess relative risk (ERR): The ratio between the total risk, including the increase due to radiation exposure, and the baseline risk in the absence of radiation exposure; if the excess equals the baseline the relative risk is two.

exposure (technical use): A measure of the ionization produced in air by x or gamma radiation. Exposure is the sum of electric charges on all ions of one sign produced in air when all electrons liberated by photons in a volume of air are completely stopped, divided by the mass of the air in the volume. The unit of exposure in air is the roentgen (R) or in SI units it is expressed in coulombs (C), 1 R = 2.58 x 10–4 C/kg.

exposure (non-technical use): the presentation of an individual or material to radiation likely to deliver a significant dose over a period of time.

EVA: extravehicular activity.

excess risk: the increase in the probability of a certain effect on an individual who has been exposed to a given dose of radiation over the probability of that effect in the absence of radiation exposure.

extravehicular activity: Any activity undertaken by the crew outside a space vehicle or habitat.

Back to top


favorable propagation path: A concept suggesting that the Archimedean spiral path from the earth to the sun would connect to a specific solar longitude. It is based on the concept that charged particles travel along the interplanetary magnetic field which is transported out from the sun. For an idealized constant speed solar wind flow, if the interplanetary magnetic field is frozen in the plasma, then the result would form an Archimedean spiral.

FEMA: Federal Emergency Management Agency.

FIRE: First ISCCP Regional Experiment.

first ionization potential: The energy required to remove the least bound electron from an electrically neutral atom. (The ionization potential is usually given in electron volts.)

FISH: fluorescence in situ hybridization.

fluence: (1) ICRU definition : The quotient of dN by da, where dN is the number of particles incident on a sphere of cross-sectional area da (i.e., Φ = dN/da). The unit for fluence is 1/m2, but cm–2 is frequently used; (fluence may be a function of one or more other variables [e.g., Φ (L,t), the distribution of fluence as a function of linear energy transfer (L) and time (t)]. (2) planar fluence (F): The net number of charged particles traversing a given area. Unit: particles/cm2.

fluence rate (dF/dt): Change in fluence over a given small time interval, or the time derivative of the fluence. Unit: 1/m2s.

FLUKA: a general purpose Monte-Carlo computer code for calculations of particle transport and interactions with matter

flux ): Term used historically by the nuclear community for fluence rate and also used for particle flux density, but deprecated by the ICRU convention to eliminate confusion between the terms “particle flux density” and “radiant flux.” See fluence rate.

FM: frequency modulation.

FR: fixed-ratio.

fractionation: The delivery of a given total dose of radiation as several smaller doses, separated by intervals of time.

FSP: fission surface power.

FY: Fiscal Year.

Back to top


galactic cosmic rays: the components of galactic cosmic radiation.

galactic cosmic radiation (GCR): The charged-particle radiation outside the Earth magnetosphere comprised of 2 % electrons and positrons, and 98 % nuclei, the latter component consisting (by fluence) of 87 % protons, 12 % helium ions, and 1 % high atomic number, high-energy (HZE) particles.

gamma rays: Short-wavelength electromagnetic radiation of nuclear origin (approximate range of energy: 10 keV to 9 MeV).

GCR: galactic cosmic radiation/ galactic cosmic rays.

GCR: galactic cosmic radiation.

GEANT: A computer application for the simulation of the passage of particles through matter including detector description and simulation.

GEO: Geostationary or Geosynchronous Earth Orbit.

Geostationary Operational Environmental Satellite ( GOES): A satellite in geosynchronous orbit used for monitoring protons. The satellite travel at the same angular speed above the equator as Earth’s rotation and therefore appears stationary when observed from Earth’s surface.

GGTP: gamma-glutamyl transpeptidase.

GI: gastrointestinal.

GLE: ground level event.

GM: geometric mean.

GPM: Global Precipitation Measurement.

gray (Gy): The International System (SI) unit of absorbed dose of radiation, 1 Gy = 1 J kg–1.

gray equivalent (GT or Gy-Eq): The product of DT and Ri, where DT is the mean absorbed dose in an organ or tissue and Ri is a recommended value for relative biological effectiveness for deterministic effects for a given particle type i incident on the body ( GT = Ri × DT). The SI unit is J/kg (NCRP, 2000).

GSD: geometric standard deviation (the standard deviation of the logarithms of a set of random variables, for which the geometric mean is the square root of their product.

GSI(Gesellschaft für Schwerionenforschung): Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany.

GSM: global system for mobile communications.

GT: gray equivalent.

Back to top


HACD: Human Adaptation and Countermeasures Division.

HDPE: high-density polyethylene, defined as having a density greater than 0.94 g/cm3.

heavy charged particles: Atomic and subatomic charged particles with masses substantially heavier than that of an electron.

heavy ions: Nuclei of elements heavier than helium such as nitrogen, carbon, boron, neon, argon or iron which are positively charged due to some or all of the atomic electrons having been stripped from them.

HEDS: Human Exploration and Development of Space.

HEFD: Habitability and Environmental Factors Division.

heliocentric: A measurement system with its origin at the center of the sun.

heliolongitude: Imaginary lines of longitude on the sun measured east (left) or west (right) of the central meridian (imaginary north-south line through the middle of the visible solar disk) as viewed from Earth. The left edge of the solar disk is 90°E and the right edge is 90°W.

heliosphere: The magnetic bubble containing the solar system, solar wind, and entire solar magnetic field. It extends beyond the orbit of Pluto.

HEPAD: High Energy Proton and Alpha Detector.

HIDH: Human Integration Design Handbook; NASA/SP-2010-3407

high atomic number, high-energy ( HZE) particles: Heavy ions having an atomic number greater than that of helium (such as nitrogen, carbon, boron, neon, argon or iron ions that are positively charged) and having high kinetic energy.

high-LET: Radiation having a high-linear energy transfer; for example, protons, alpha particles, heavy ions, and interaction products of fast neutrons.

HIMAC: Heavy Ion Medical Accelerator, Chiba Japan.

HMF: heliospheric magnetic field.

HPC: Hydrological Process and Climate.

HPRT: hypoxanthine-guanine phosphoribosyl transferase.

HQ: Headquarters.

HRP: Human Research Program.

HRP CB: Human Research Program Control Board.

HSIR: Constellation Program Human Systems Integration Requirements; CxP 70024

H T : equivalent dose.

HZE: high atomic number and energy.

HZETRN: a transport code developed specifically for high-charge, high-energy particles that is widely used for space radiation shielding and design calculations.

HZE: high atomic number, high energy/ highly energetic, heavy, charged particles.

Back to top


IACUC: Institutional Animal Care and Use Committee.

IAEA: International Atomic Energy Agency.

ICNIRP: International Commission on Non-Ionizing Radiation Protection.

ICRP: International Commission on Radiation Protection.

ICRU: International Commission on Radiation Units and Measurements.

IDIQ: Indefinite delivery/indefinite quantity.

IEEE: Institute of Electrical and Electronics engineers.

IL-2: interleukin-2.

IL-6: interleukin-6.

incidence: The rate of occurrence of a disease, usually expressed in number of cases per million .

IND: improvised (or otherwise acquired) nuclear device.

interplanetary magnetic field: The magnetic field in interplanetary space. The interplanetary magnetic field is transported out from the sun via the solar wind.

interplanetary shocks: An abrupt change in the velocity or density of charged particles moving faster than the wave propagation speed in interplanetary space, so that higher velocity components bunch into lower velocity components before these can get out of the way.

ionizing radiation: Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.

ionization: The process by which a neutral atom or molecule acquires a positive or negative charge through the loss or gain of one or more orbital electrons.

IPT: Integrated Product Team.

IRMA: Integrated Risk Management Application.

ISCCP: International Satellite Cloud Climatology Project.

ISS: International Space Station.

ISSMP: ISS Medical Project.

ITA: Internal Task Agreement.

IVCPDS: Intra Vehicle Charged Particle Directional Spectrometer

IV & V: Independent Validation & Verification.

IWG: Investigator Working Group.

IWS: Investigator Workshop.

Back to top


JSC: NASA Johnson Space Center.

JWST: James Webb Space Telescope.

Back to top


kerma: (an acronym for “Kinetic energy released in materials;” the sum of the initial kinetic energies for all charged particles released by uncharged ionizing radiation in a small sample of material divided by the mass of the sample. Kerma is the same as dose when charged particle equilibrium exists (i.e., when, on the average, the number of charged particles leaving the sample is compensated by an equal number of charged particles entering the sample).

Back to top


LAP: latency associated peptide.

LAR: lifetime attributable risk.

LaRC: NASA Langley Research Center.

LAT: Lunar Architecture Team.

latchup: an anomalous state in a semiconductor in which the device no longer responds to input signals.

latent period: Period or state of seeming inactivity between time of exposure of tissue to an injurious agent and an observed response (also time to response or induction period).

LBNL: Lawrence Berkeley National Laboratory.

LCD: liquid crystal display.

LCVG: liquid cooling and ventilation garment.

LDEF: Long Duration Exposure Facility.

LDL: low-density lipoproteins.

LEND: Low Energy Neutron Detector.

LEO (low Earth orbit): the environment in which most recent space missions have been concentrated, where the magnetic field of Earth provides protection against much of the radiation that would be encountered on more distant exploration missions, approximately 300 to 600 mile orbit radius.

LET (linear energy transfer): Measure of the average local energy deposition per unit length of distance traveled by a charged particle in a material. Unit: keV/μm.

lifetime risk: The lifetime probability of suffering from the consequences of a specific health effect. The total risk in a lifetime resulting from an exposure(s) is equal to the average annual risk times the period of expression.

light ions: Nuclei of hydrogen and helium which are positively charged due to some or all of the planetary electrons having been stripped from them.

lineal energy ( y ): The quotient of ε by , where ε is the energy imparted to the matter in a given volume by a single (energy deposition) event and is the mean chord length of that volume ( i.e., y = ε/ l ). The unit for lineal energy is J /m, but keV/ μm is often used in practice (1 keV/µm ~ 1.6x10-10 J/m).

linear energy transfer ( LET): Average amount of energy lost per unit of particle track length as an ionizing particle travels through material, related to the microscopic density distribution of energy deposited in the material and, therefore, a major characteristic of radiation leading to different effects for the same dose of ionizing radiation of different LET on biological specimens or electronic devices.

linear-quadratic model (also linear-quadratic dose-response relationship): expresses the incidence of (e.g., mutation or cancer) as partly directly proportional to the dose (linear term) and partly proportional to the square of the dose (quadratic term).

LIS: local interstellar energy spectrum.

LIS: local interstellar GCR spectrum.

LIS: Local interplanetary Spectra.

LLD: lower limit of detection.

LLU: Loma Linda University.

LLO: low lunar orbit.

lognormal: If the logarithms of a set of values are distributed according to a normal distribution the values are said to have a lognormal distribution, or be distributed log normally.

low-LET: Radiation having a low-linear energy transfer; for example, electrons, x rays, and gamma rays.

LRV: Lunar Roving Vehicle.

LSAC: Life Sciences Applications Advisory Committee.

LSS: Life Span Study.

LSS: Life-Span Study of the Japanese atomic-bomb survivors.

Lunar Lander: the Constellation system vehicle that will travel between the Orion and the surface of the Moon.

LWS: Living With a Star (a NASA program).

Back to top


MARIE: Mars Radiation Environment Experiment.

mass stopping power: (see stopping power ).

MAT: Mars Architecture Team.

MCNPX: Monte Carlo N-Particle eXtended.

MDO: Multi-disciplinary Optimization.

mean absorbed (tissue) dose ( DT): The mean absorbed dose in an organ or tissue, obtained by integrating or averaging absorbed doses at points in the organ or tissue.

mean-free path: The average distance between particle collisions with nuclei, atoms or molecules in a material. Also, the average distance between scattering events in interplanetary particle propagation.

MEEP: Mir Environment Effects Payload.

MEO: Medium Earth Orbit.

MeV: Mega-electron Volts: 106 electron volts

mFISH: Multiplex Fluorescence In Situ Hybridization.

Mir: The Russian (previously Soviet) orbital space station.

MISSE: Materials on International Space Station Experiment.

MML: mouse myelogenous leukemia.

MMOP: Multilateral Medical Operations Panel.

MOA: Memorandum of Agreement.

MODIS: Moderate Resolution Imaging Spectrometer.

MORD: Medical Operations Requirements Documents.

MOU: Memorandum of Understanding.

Mrem: millirem.

MRI: magnetic resonance imaging.

MS: Mission Systems

mSv: millisievert.

Back to top


N: nucleon.

NAR: Non-Advocate Review.

NAS: National Academy of Sciences.

NASA: National Aeronautics and Space Administration.

NCI: National Cancer Institute.

NCRP: National Council on Radiation Protection and Measurements.

NEDD: Constellation Program Natural Environment Definition for Design; CxP 70044

neutrons: Particles with a mass similar to that of a proton, but with no electrical charge. Because they are electrically neutral, they cannot be accelerated in an electrical field.

NIEL: Non-ionizing energy loss, also called displacement kerma. The total kerma can be divided into an ionizing component and a displacement, or NIEL, component.

NIH: National Institutes of Health.

NM: neutron monitor.

NOAA: National Oceanic and Atmospheric Administration.

noncancer: Health effects other than cancer (e.g., cataracts, cardiovascular disease) that occur in the exposed individual.

Nowcasting: prediction of total doses and the future temporal evolution of the dose once a solar particle event has begun.

NOVICE: Radiation Transport/Shielding Code.

NPR: NASA Procedural Requirements.

NRA: NASA Research Announcement.

NRC: National Research Council.

NRC: Nuclear Regulatory Commission (US).

NSBRI: National Space Biomedical Research Institute.

NSCOR: NASA Specialized Center of Research.

NSF: National Science Foundation.

NSRL: NASA Space Radiation Laboratory (at BNL).

NTE: Non-Targeted Effects.

Back to top


OBPR: Office of Biological and Physical Research.

OCHMO: Office of Chief Health and Medical Officer.

organ dose equivalent ( DET): The mean dose equivalent for an organ or tissue, obtained by integrating or averaging dose equivalents at points in the organ or tissue. It is the practice in the space radiation protection community to obtain point values of absorbed dose (D) and dose equivalent (H) using the accepted quality factor-LET relationship [Q(L)], and then to average the point quantities over the organ or tissue of interest by means of computational models to obtain the organ dose equivalent (DET ). For space radiations, NCRP adopted the organ dose equivalent as an acceptable approximation for equivalent dose (HT) for stochastic effects.

Orion Crew Exploration Vehicle: The Constellation system vehicle that will carry passengers in low Earth orbit, or from low Earth orbit to the Moon or Mars, and then back to Earth. Often referred to as CEV; in this report referred to as the Orion crew module.

OSHA: Occupational Safety and Health Administration.

Back to top


PC: Probability of Causation.

PCC: premature chromosome condensation.

PCS: personal communication system.

PDF: probability density function.

PDF: probability distribution function.

PE: Project Executive.

PEL (permissible exposure limit): Maximum amount of radiation to which an astronaut may be exposed. For terrestrial workers, PELs are legal limits, defined by OSHA. NASA PELs are set by the chief health and medical officer.

PET: positron emission tomography.

photosphere: The portion of the sun visible in white light. Also the limit of seeing down through the solar atmosphere in white light.

PI: Principal Investigator.

PLR: pressurized lunar rover.

PLSS: personal life support system.

PM: Project Manager.

PP: Project Plan.

PPBE: Planning, Programming, Budgeting and Execution.

PPS: proton prediction system/ pulses per second.

PRD: Passive Radiation Detector; Program Requirements Document.

prevalence: The number of cases of a disease in existence at a given time per unit of population, usually per 100,000 persons.

protons: The nucleus of the hydrogen atom. Protons are positively charged.

protraction: Extending the length of exposure, for example, the continuous delivery of a radiation dose over a longer period of time.

PS: Project Scientist.

PSD: Position-Sensitive Detector; also, Pulse Shape Discrimination.

PVAMU: Prairie View A&M University.

PW: pulsed wave.

Back to top


Q: quality factor.

Q(L): quality factor as a function of linear energy transfer.

Qleukemia: quality factor for estimating leukemia risks.

Qsolid: quality factor for estimating solid cancer risks.

QMSFRG: quantum multiple scattering fragmentation model.

quality factor ( Q ): The factor by which absorbed dose (D) at a point is modified to obtain the dose equivalent (H) at the point (i.e., H = Q D), in order to express the effectiveness of an absorbed dose (in inducing stochastic effects) on a common scale of risk for all types of ionizing radiation. There is a specified dependence [Q(L)] of the quality factor (Q) as a function of the unrestricted linear energy transfer (L) in water at the point of interest.

quasithreshold dose: The dose at which the extrapolated straight portion of the dose-response curve intercepts the dose axis at unity survival fraction.

Back to top


RAD: Radiation Assessment Detector.

RAM: Radiation Area Monitor.

radiation: 1. The emission and propagation of energy through space or through matter in the form of waves, such as electromagnetic, sound, or elastic waves; 2. The energy propagated through space or through matter as waves; radiation or radiant energy, when unqualified, usually refers to electromagnetic radiation; commonly classified by frequency— Hertzian, infrared, visible, ultraviolet, x and gamma rays; 3. Corpuscular emission, such as alpha and beta particles, or rays of mixed or unknown type, such as cosmic radiation.

radiation quality: A general term referring to the microscopic distribution of of the energy absorbed to yield a given total dose. For example, at resolutions of a few micrometers ionizing events will be more uniformly dispersed for gamma-ray radiation than for the neutron radiation, producing quantitatively different biological effects (see relative biological effectiveness ).

radiation weighting factor ( wR): A factor related to the relative biological effectiveness of different radiations in the calculation of equivalent dose (HT) (see equivalent dose ), independently of the tissue or organ irradiated.

RBE (relative biological effectiveness): Measure of the effectiveness of a specific type of radiation for producing a specific biological outcome, relative to a reference radiation (generally, 250 kVp x-rays). For a defined endpoint, RBE = Dref/Dnew. For HZE particles, RBE generally is greater than 1, meaning that a lower dose of more effective HZE particles will have the same effect as a given dose of the reference radiation.

RCT: Radiation Coordination Team.

RDD: radiological dispersal device.

RDWG: Radiation Discipline Working Group.

regolith: A layer of loose, heterogeneous material covering solid rock on the surface of a moon or planet (including Earth).

REIC: risk of exposure-induced cancer incidence.

REID (risk of exposure induced death): Measure of risk used by NASA as a standard for radiation protection; reflects a calculation of the probability of death due to exposure to radiation in space.

relative biological effectiveness (cf. RBE)

relative risk (cf. excess relative risk)

REM: rapid eye movement.

RF: radiofrequency.

RFI: request for information.

RHIC: Relativistic Heavy Ion Collider (at BNL).

RHO: Radiation Health Officer.

rigidity: The momentum of a charged particle per unit charge. Determines the curvature of the particle’s trajectory in a magnetic field. Two particles with different charge but the same rigidity will travel along a path having the same curvature in a given magnetic field.

risk: The probability of a specified effect or response occurring.

risk coefficient: The increase in the annual incidence or mortality rate per unit dose: (1) absolute risk coefficient is the observed minus the expected number of cases per person year at risk for a unit dose; (2) the relative risk coefficient is the fractional increase in the baseline incidence or mortality rate for a unit dose.

risk cross section: The probability of a particular excess cancer mortality per particle fluence (excluding delta rays).

risk estimate: The number of cases (or deaths) that are projected to occur in a specified exposed population per unit dose for a defined exposure regime and expression period; number of cases per person-gray or, for radon, the number of cases per person cumulative working level month.

roentgen: A unit of radiation exposure. Exposure in SI units is expressed in C kg–1 of air.

ROS: reactive oxygen species.

RRS: radiation Research Society.

RSNA: Radiological Society of North America.

R&T: Research and Technology.

RTG: radioisotope thermoelectric generator.

Back to top


SAA: South Atlantic Anomaly.

SACR: Science Advisory Committee on Radiobiology.

SAMPEX: Solar Anomalous and Magnetospheric Particle Explorer.

SAR: specific absorption rate.

SBIR: Small Business Innovation Research.

SCAR: Smoke/Sulfate Clouds and Radiation Experiment.

SCC: squamous cell carcinoma/ small cell cancer.

SCE: sister chromatid exchange.

SCLS: small cell lung carcinoma.

SD: single dose.

SD: standard deviation.

SDO: Solar Dynamic Observatory.

SEC: Space Environment Center. (NOAA).

secondary radiation: radiation that has been generated by the interaction of radiation with the atoms or nuclei of a traversed material.

SEE (single-event effect): a class of effects in which damage results from a single ionizing particle traversing a microelectronic device, rather than the accumulated impact of a large number of particles.

SEE: single event effect/ Space Environment and Effects Program.

SEER: surveillance, epidemiology, and end results.

SET: Space Environment Testbeds.

SEU (single event upset): a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device.

SFHSS: Space Flight Human Systems Standard; NASA-STD-3001

SGZ: subgranular zone.

SI: International System of Units.

sievert ( Sv): The special name for the SI unit of effective dose (E), equivalent dose (HT), dose equivalent (H), and organ dose equivalent (DT ), 1 Sv = 1 J /kg.

SLSD: Space Life Sciences Directorate (NASA).

S&MA: Safety and Mission Assurance (NASA).

SMD: Science Mission Directorate (NASA).

SMO: Science Management Office (NASA).

SOHO: Solar and Heliospheric Observatory.

Solar cycle: The periodic variation in the intensity of solar activity, as measured, for example, by the numbers of sunspots, flares, CMEs, and SPEs. The average length of solar cycles since 1900 is 11.4 y.

solar flare: The name given to the sudden release of energy (often >1032 ergs) in a relatively small volume of the solar atmosphere. Historically, an optical brightening in the chromosphere, now expanded to cover almost all impulsive radiation from the sun.

solar-particle event (SPE): An eruption at the sun that releases a large number of energetic particles (primarily protons) over the course of hours or days. Signatures of solar energetic-particle events may include significant increases in types of electro­magnetic radiation such as radio waves, x-rays, and gamma rays.

solar wind: The plasma flowing into space from the solar corona. The ionized gas carrying magnetic fields can alter the intensity of the interplanetary radiation.

SOMD: Space Operations Mission Directorate (NASA).

spallation: A high-energy nuclear reaction in which a high-atomic-number target nucleus is struck by a high-energy, light particle (typically a proton); this causes the target nucleus to break up into many components, releasing many neutrons, protons, and higher Z particles.

SPE (cf. solar particle event).

Space Radiation Analysis Group (SRAG): the radiation protection group at NASA’s Johnson Space Center, responsible for radiation monitoring, projecting exposures, and ensuring adherence to principles of ALARA for crews on spaceflight missions.

SPENVIS (SPace ENVironment Information System) : a series of computer programs developed by the European Space Agency for the simulation of radiation effects in flight.

SRA: Society for Risk Analysis.

SRAG: Space Radiation Analysis Group

sRBC: Serum deprivation response factor-related gene product that binds to C-kinase.

SRPE: Space Radiation Program Element (NASA).

SSA: Social Security Administration.

STEREO: Solar-Terrestrial Relations Observatory (NASA mission).

stochastic effects: radiation effects attributed to the consequences of changes caused by radiation in one or a few cells; so called because the statistical fluctuations in the number of initial cells are large compared to the number of cells observed when radiation effects, such as cancer, become manifest (ICRP 1991). The probability of occurrence, rather than the severity, is a function of radiation dose.

stochastic process: process whereby the likelihood of the occurrence of a given event can be described by a probability distribution.

stopping power (lineal stopping power): The quotient of the energy lost (dE) by a charged particle in traversing a distance (dx) in a material. Can also be expressed as mass stopping power by dividing the lineal stopping power by the density (ρ) of the material.

STS: Space Transportation System.

STTR: Small Business Technical Transfer Research.

Back to top


TEDE: total effective dose equivalent.

TEPC: tissue equivalent proportional counter.

TGF: transforming growth factor.

TIGER: Grid Generation Code.

tissue weighting factor ( wT): A factor representing the ratio of risk of stochastic effects attributable to irradiation of a given organ or tissue to the total risk when the whole body is irradiated uniformly. The factor is independent of the type of radiation or energy of the radiation.

TLD: thermoluminescent dosimeter.

TMG: thermal micrometeoroid garment.

TMI: Three Mile Island.

TOGA/COARE: Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Experiment.  transport (of radiation): the sequence of interactions between radiation traversing one or more materials and their atoms and nuclei; calculations of the relevant characteristics; transport code: computer program to calculate radiation transport.

trapped radiation: Ionized particles held in place by Earth’s magnetic fields. Also known as the Van Allen belt.

TRL: Technology Readiness Level.

TRMM: Tropical Rainfall Measuring Mission.

TVD: tenth-value distance.

TVL: tenth-value layer.

Back to top


UNSCEAR: United Nations Scientific Committee on the Effects Of Atomic Radiation.

US: United States.

USAF: United States Air Force.

US NRC: United States Nuclear Regulatory Commission.

USRA: Universities Space Research Association.

UV: ultraviolet.

Back to top


vitreous: The semifluid, transparent substance which lies between the retina and the lens of the eye.

VSE: Vision for Space Exploration.

Back to top


WBS: Work Breakdown Structure.

WHO: World Health Organization.

Wind: a NASA spacecraft that observes the Sun and solar wind.

WL: working level.

WLM: working level month (170 h).

w R: radiation weighting factor.

w T: tissue weighting factor.

Back to top




Z: atomic number, the number of protons in the nucleus of an atom.

Back to top

Site Map


THREE Encyclopedia





Viewing Slide Presentations

Statement of Policies

Space Radiation Program Element

Contact Us

The web site is produced for NASA’s Space Radiation Program Element.  Your input is welcome. Please send your comments and articles along with your full name, address, institution, and e-mail address to, or you may use the form provided.