Space Radiation and Astronaut Health Managing and Communicating Cancer Risks (2021) / Chapter Skim
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Assessing, managing, and communicating radiation risks for space exploration is challenging because of incomplete knowledge of the complicated radiation environment in space, limited data on the cellular damage mechanisms resulting from radiation, absence of direct observations resulting from epidemiological studies, individual characteristics affecting susceptibility, and complex concepts associated with radiation risk ascertainment. Beyond the protection of Earth's magnetic field, astronauts are exposed to a complex radiation environment composed of galactic cosmic rays (GCR)
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. NASA'S CURRENT SPACE RADIATION HEALTH STANDARD The NASA Space Permissible Exposure Limit for Spaceflight Radiation Exposure Standard 4.2.10 ("the standard")
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Provide a written report with recommendations on the best process and strategies for NASA to use in addressing and managing the uncertainties of long-term cancer risks due to radiation exposure in crewed space missions beyond low Earth orbit. In conducting the review, the committee will consider the following: • N ASA's present processes for assessing uncertainty from radiation risk exposure in crewed space missions compared to terrestrial methods for clinical applications, and how data from ground-based research on the relationship between radiation exposure and cancer risk should inform NASA's approach to risk management for crewed missions.
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For example, in this report, 3 percent REID implies that within a cohort of 100 astronauts, 3 are likely to die of radiation-induced cancer at some point in their lifetime. The current standard is intended to apply only to radiation exposure incurred during missions in low Earth orbit (LEO)
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NASA is also aware that recent updates from epidemiological and radiobiological studies on sex differences in radiation-induced cancer risks may affect its cancer risk assessment model and what is an acceptable level of radiation exposure for astronauts. NASA is seeking advice on the longstanding con cern that the current radiation standard results in an unequal work envi ronment that limits female astronauts to shorter space careers because of scientific data indicating that females have an increased risk of cancer from exposure to ionizing radiation compared to men.
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above the non-exposed baseline mean. Individual astronaut career dose includes all past spaceflight radiation exposures, NASA biomedical research exposures, plus the projected exposure for an upcoming mis sion.
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COMMITTEE'S ANALYSIS OF NASA'S PROPOSED SPACE RADIATION EXPOSURE HEALTH STANDARD The committee's analysis includes scientific and ethical considerations related to the components that make up the proposed revised standard as well as the implications of their relationship and combination as part of a new health standard. Considering the Interconnected Components of the Proposed Standard REID informs or serves as the basis for the three components of the proposed revised radiation standard.
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Such a single standard would provide equality of opportunity, at least to the extent that it avoids radiation exposure standards that differ by sex and result in differential opportunities for participation in crewed spaceflights. Principles of compensatory justice and distributive justice are also served by a single standard.
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The committee notes that NASA's proposal to set the permissible dose based on the mean, while maintaining the 3 percent REID limit previously applied to the 97.5th percentile, results in a higher dose than the current standard. This higher probability of harm seems to conflict with an ethics commitment to protection from harm, minimization of risk, and NASA's requirement to ensure astronaut safety by keeping exposures as low as reasonably achievable (ALARA)
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Combined Implications of NASA's Proposed Radiation Health Standard In NASA's proposed radiation health standard, career thresholds are driven by mean REID calculations for a 35-year-old female and would be applied to all astronauts, regardless of sex and age. The effective dose equivalent to 3 percent REID, for a 35-year-old female, is ~600 mSv (although NASA notes that values presented are approximate, +/– 10 percent, and will be verified prior to establishing a new standard)
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or other metrics, or a combination of metrics, in setting the dose-based space radiation health standard. NASA should conduct an independent analysis of the validity of 3 percent REID and make explicit the agency's justification for the metrics it chooses.
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The committee reached the following conclusion regarding NASA's consideration of revisions to the current radiation exposure standard: Conclusion I: The committee concludes that astronauts who travel on long-duration spaceflight missions are likely to be exposed to radiation levels that exceed the proposed new space radiation standard of an effective dose of 600 mSv. For example, a mission to Mars is likely to exceed the exposure standard by up to 150 per cent.
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FIGURE S-2 NASA's proposed system for communicating its proposed space permissible exposure limit for spaceflight radiation exposure standard. NOTE: CI = confidence interval; mSv = millisievert; NASA = National Aeronautics and Space Administration; REIC = risk of exposure-induced cancer; REID = risk of exposure-induced death.
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While NASA astronauts are the primary audience for communication of radiation exposure risks, other audiences will also be recipients of this communication. Audiences outside of NASA may not have the same technical background as NASA personnel and might interpret and react differently to figures, data, and information about radiation-induced cancer risks.
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, inclusion of the waiver process suggests that an exception to the standard is built into the standard and its application. Communicating an Individual Risk Assessment to an Astronaut The committee makes the following recommendations regarding NASA's strategies for communicating individual radiation-induced cancer risks.
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• Provide astronauts with easy access to summary information regard ing what is known about the cancer risk factors that might interact with radiation exposures to influence long-term health outcomes for astronauts. RISK COMMUNICATION AND NASA'S WAIVER PROCESS NASA has acknowledged that with current technology, a mission to Mars would expose all astronauts to space radiation that exceeds
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In this instance, unlike employers subject to Occupational Safety and Health Administration standards, NASA may seek to obtain permission for a mission waiver that would permit the agency to subject all volunteers for that mission to an unusual level of risk that would be unacceptable in less time-sensitive and critical missions. Waivers for specific missions and for individual participation in any given mission were considered in depth by the 2014 IOM Committee on Ethics Principles and Guidelines for Health Standards for Long Duration and Exploration Spaceflights.
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Risk Communication Research Agenda for NASA Given the unique needs and characteristics of spaceflight programs and astronaut populations, NASA would benefit from engaging in risk communication evaluation and research to better understand and improve the effectiveness of their communication strategies. The committee makes the following recommendation regarding a NASA risk communication research agenda: Recommendation 6: NASA should conduct research to develop evidence-based risk communication and the agency should develop a radiation risk communication research agenda to fill knowledge gaps such as (1)
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