Method of estimating lifetime cancer risk due to chronic radionuclide intake

A methodology for computing the cancer risk due to chronic radionuclide intake, assuming that cancer risk functions per unit dose as a function of age are known, is presented. In this work, an age-dependent intake function is assumed, the total amount of activity present in the body at any given age is computed, and the annual dose equivalent or effective dose estimated using age-dependent dose conversion factors. In a series of time intervals extending from the age of intake to age 80 y, the radiation-induced cancer mortality is estimated by multiplying the dose in any given year by the cancer risk per unit dose at a given age. By integrating the product of the dose and the risk at each time interval, the overall risk due to various chronic radionuclide intake scenarios over a lifetime is determined. This result is compared to the risk computed using integrated committed dose quantities and to the risk computed from an age-independent risk per unit dose. The example cases of dietary contamination following a nuclear incident and uranium contamination in drinking water are presented. The results show that ignoring the age dependence of the dose-risk relationship underestimates the total lifetime risk by more than 80% for the dose due to ¹³⁷Cs in milk in a nuclear incident scenario. Furthermore, it is found that if the integrated committed dose quantity is used to evaluate risk, the total risk will be overestimated by almost 50% in the case of chronic uranium ingestion. These results demonstrate the sensitivity of the total lifetime risk to the proper assignment of dose to each time interval and to the use of age-dependent risk coefficients.