Space Radiation and Astronaut Health Managing and Communicating Cancer Risks (2021) / Chapter Skim
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3 NASA's Spaceflight Radiation Exposure Standard
3 NASA's Spaceflight Radiation Exposure Standard
Pages 51-70
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From page 51... ...
NASA's Space Permissible Exposure Limit for Space Flight Radiation Exposure Standard 4.2.10 ("the standard") informs crew mission assignments, crew health care (preflight, in-flight, and postflight)
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From page 52... ...
RADIATION EXPOSURE STANDARDS USED BY OTHER AGENCIES Standards Used to Manage Terrestrial Radiation Exposure The objective for managing terrestrial radiation exposure is grounded on reducing the potential for the radiation detriment related to stochastic effects. The system of radiological protection as recommended by the International Commission on Radiological Protection (ICRP)
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From page 53... ...
. NASA's proposal to revise its space radiation standard in terms of effective dose based on a mean of less than 3 percent REID and applied universally for sex and age would be more consistent with the approaches of current standards used to manage terrestrial radiation exposure.
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From page 54... ...
For example, the Russian Space Agency's (RSA's) cancer risk TABLE 3-1 Radiation Exposure Career Limits Summary: International Space Station Partner Agencies Space Agency Career Limit Sex/Age Dependency Canadian Space Agency 1,000 mSv No sex or age dependency European Space Agency 1,000 mSv No sex or age dependency Russian Space Agency 1,000 mSv No sex or age dependency Japanese Aerospace Exploration 3 percent REID @ Yes Agency the mean Lower limit: 500 mSv for 27- to 30-year-old female Upper limit: 1,000 mSv for > 46-year-old male National Aeronautics and Space 3 percent REID Yes Administration (current)
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From page 55... ...
To the committee's knowledge, only NASA has a process for granting a waiver to an astronaut that would allow him or her to fly on a mission that exceeds the career limit. The other agencies acknowledge that a waiver process may be needed as they plan for long-duration missions.2 NASA'S PROPOSED SPACE RADIATION EXPOSURE HEALTH STANDARD NASA provided the committee with details about the proposed changes to its space radiation exposure standard including draft language for section 4.2.10.1 of the standard (see Box 3-1)
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From page 56... ...
Before moving to a discussion of the committee's analysis of the proposed changes to the space radiation standard, it is important to begin with an overview of the basis for NASA's current space radiation standard. THE BASIS FOR NASA'S CURRENT SPACE RADIATION EXPOSURE STANDARD In 1970, the National Academies' Space Studies Board made recommendations to NASA for guidelines for career doses for long-term 3 NASA has indicated that the proposed limit of 600 mSv is an approximate value.
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From page 57... ...
Following the recommendation of NCRP Report 98 (1989) , which provided guidance to NASA concerning radiation protection in LEO, the NASA space radiation standard has been set at 3 percent REID for both sexes and all ages since 1995.
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From page 58... ...
. 5 Though the career exposure limit is 3 percent REID, NASA currently uses the "admin istrative limit" of 1 percent REID to meet the 3 percent standard at a 95 percent confidence interval (Semones, 2021)
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From page 59... ...
Considering 3 Percent REID NASA's limit of 3 percent REID was taken as a starting point for this committee's work as it was not part of the study task to consider NASA's underlying risk model or the use of any particular REID limit. While 3 percent REID has been used by NASA since the 1989 NCRP report, the committee discussed that it may be time for NASA to reconsider the level of REID on which to base the standard.
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From page 60... ...
In summary, the committee believes an important, near-term opportunity exists for NASA to conduct an independent analysis of the validity of a 3 percent REID. COMMITTEE'S ANALYSIS OF NASA'S PROPOSED SPACE RADIATION EXPOSURE HEALTH STANDARD NASA requested that this committee review and assess NASA's proposed process and strategies for managing the risk of cancer due to exposure to space radiation (i.e., NASA's proposed changes to the space radiation health standard)
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From page 61... ...
It is the decisions about selection of the age and sex on which to base the standard and choices made in using the 3 percent REID to determine the level of acceptable risk that determine whether dose exposure limits would be increased or decreased compared to the current standard. The combination of choosing to calculate the exposure threshold based on 35-year-old females or other age/sex category, and using the mean, median, 95 percent, or 75 percent confidence level will in combination have the effect of changing the acceptable dose limit when calculated based on 3 percent REID.
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From page 62... ...
It is also the case that terrestrial occupational health radiation dose-limiting standards apply irrespective of gender. NASA moving to a single standard is consistent with standard occupational health practice, although there are notable differences between NASA's other proposed changes to the radiation health standard and occupational health practice.
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From page 63... ...
The committee provides this rationale in more detail in Chapters 2 and 4. The committee notes that NASA's proposal to set the permissible dose based on the mean allows for greater dose than the current standard while continuing to use 3 percent REID.
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From page 64... ...
To reiterate, the three components, or decisions, embedded in NASA's proposed updates to the radiation health standard do not exist in isolation -- each component, or decision, interacts with the others such that changing one component results in changes to the overall standard. For example, if NASA had utilized a 35-year-old female as the basis for the new standard, but derived the dose from 3 percent REID by the current methodology of 97.5 percent confidence level, there would be no change to the allowable exposure for a 35-year-old female, but the allowable dose for a 55-year-old male would decrease.
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From page 65... ...
a single standard with dose limits based on risk to 35-year-old females comes at the expense of potential greater allowable exposures for some older and male astronauts, which could be seen as an unfair restriction of opportunity for them. Taken together, the proposed standard creates equality of opportunity for spaceflight with the trade-offs of somewhat higher allowable exposure to radiation for a subset of astronauts (primarily women)
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From page 66... ...
The committee makes the following recommendations regarding NASA's proposed space radiation health standard: Recommendation 1: NASA should proceed with the proposed a pproaches to revising the space radiation health standard. As proposed by NASA, the agency should: • Apply a single space radiation standard to all astronauts; • Utilize the most protective approach in setting the space radiation standard; • Set the standard as a dose limit; and • Utilize the mean value of the risk distribution based on 3 percent risk of exposure-induced death.
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From page 67... ...
The committee reached the following conclusion regarding NASA's proposed space radiation health 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 mis sion to Mars is likely to exceed the exposure standard by up to TABLE 3-3 Projected Radiation Risks for Astronauts on Lunar and Mars Missions Fatal risk, % (95% CI)
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From page 68... ...
Presentation to the Committee on Assessment of Strategies for Managing Cancer Risks Associated with Radiation Exposure During Crewed Space Missions, April 14. https://www.
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From page 69... ...
Presentation to the Committee on Assess ment of Strategies for Managing Cancer Risks Associated with Radiation Exposure During Crewed Space Missions, January 25. Semones, E
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