possible, to reduce the dose and dose rate from bremsstrahlung to the lowest practical values provides a practical example. 6. Studies should be initiated promptly to define the space worker population profiles, particularly the age and sex distributions. Age-specific deaths rates from all causes, in general, and cancers, in particular, should be obtained for a worker population composition similar to that which will work in space. These studies on the SPS worker populations will then provide the data base for calculations of potential health risks of ionizing radiations in the space environment. 7. The biological effects of the HZE particle radiations must be investigated in detail in order to determine appropriate quality factors and risks from lesions unique to HZE. Interactions between high- and low-LET radiation that could occur in the space radiation environment should be considered, particularly the possibility of synergistic effects on carcinogenesis or mutagenesis. 8. The health effects of exposure to low-level ionizing radiations must be considered in the context of the potential health effects of other physical and chemical agents in the space environment. Such competing effects may interact with other host or constitutional factors to mask, enhance, or diminish any radiation health effects, such as cancer. Environmental factors to be considered include cabin atmosphere, temperature and pressure, nutrition, non-ionizing radiation and weightlessness. This SPS Committee concludes that the radiation environment estimated for the Reference System represents a health risk to SPS workers. However, the Committee emphasizes that none of the problems identified are considered sufficiently intractable to preclude achieving a minimal risk to SPS workers. A number of areas have been considered which we believe impact on the potential health effects on workers in space. These include, for example: the biological effects of HZE particles; the effects of environmental agents in space, other than ionizing radiation, which may affect the radiation health effects; and the RBE/LET relationships. However, much more needs to be known about these factors before they may be used to improve the accuracy of quantitative estimation of health risks in space. The Committee has chosen not to include these uncertainties in its estimations at the present time but urges increased studies in these areas to provide greater precision for future SPS health assessments.
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