3. CONCLUSIONS AND RECOMMENDATIONS HEALTH RISK ASSESSMENTS For ionizing radiation, the major concern will be late or delayed health effects, particularly the increased risk of radiation-induced cancer. The estimated lifetime risk for cancer is 0.8 to 5.0 excess deaths per 10,000 workers per rad of exposure. Thus, for example, in 10,000 workers who completed ten missions with an exposure of 40 rem per mission, 320 to 2,000 additional deaths in excess of the 1640 deaths from normally occurring cancer, would be expected. These estimates would indicate a 20 to 120 percent increase in cancer deaths in the worker-population. The wide range in these estimates stems from the choice of the risk-projection model and the dose-response relationship. The choice between a linear and a linear-quadratic dose-response model may alter the risk estimate by a factor of about two. The method of analysis (e.g., relative vs absolute risk model) can alter the risk estimate by an additional factor of three. Choosing different age and sex distributions can further change the estimate by another factor of up to three. When decisions have been made about the selection of SPS workers, the precise influence of age and sex distribution can be included in later risk estimates. However, the choice of dose-response relationship and projection models is a matter of opinion and will not be resolved scientifically for quite some time. CONCLUSIONS The conclusions of the committee based on the findings above are: 1. The risk of excess cancer deaths will be doser to the lower limit estimated above because the major exposure will be from low dose rate, low-LET irradiation. This being the case, we consider a reasonable estimate to be one excess death per 10,000 workers per rem of exposure. If this level of risk is applied to the worst case reference system exposure level, namely 40 rem/mission, there would be 400 excess cancer deaths in a work force of 10,000 completing ten missions (accumulated dose equivalent of 400 rem). 2. The potential genetic consequences, which vary with the population age distribution, could be of significance. At the present time, sufficient information on the age and sex distribution of the worker population is lacking for precise estimation of impact. 3. Similarly, the radiation exposure of a pregnant worker could lead to developmental abnormalities in the embryo.
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