Uncertainties of an Age- and Time-Dependent Risk Model. S. L. Simon, Board of Radiation Effects Research, National Academy of Sciences, National Research Council, 2101 Constitution Ave., N.W., Washington, DC 20418; I. Apostoaei and F. O. Hoffman, SENES Oak Ridge, Inc., Center for Risk Analysis, 102 Donner Drive, Oak Ridge, TN 37830
The excess relative risk of radiogenic cancer is obtained from epidemiological studies based on the cumulative excess of disease over the period of time after exposure for which medical surveillance of the exposed cohorts has been carried out. A mathematical model was developed to derive numerical expressions of the excess relative risk at any moment of time after exposure. The model can be applied to individuals exposed at any age. Uncertainty and sensitivity analyses of the model have been performed for the case of thyroid cancer. This paper discusses the parameters necessary in the model and the quality of the data available to determine these parameters. The relative uncertainty in the excess relative risk per unit dose (ERR/Gy) predicted by this model varies with time since exposure. For the time periods when the excess relative risk is the largest (5 to 15 years after exposure), the relative uncertainties are the lowest; that is, the predicted ERR/Gy coefficients are reliable to use. The uncertainties are large shortly after exposure (during the latency period), and long time after exposure (more than 50 years). The same pattern is observed for other cancer types, but with different magnitudes of the uncertainty. Various ways to reduce the uncertainties are presented.
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