Estimated Risks of Radiation-induced Solid Cancers from Various Exposure Conditions and the Effects of Age and Follow-up Period on These Risks

When discussing dose-rate effects, comparing distinct epidemiological studies is important. Excess relative risks calculated under various analysis conditions in distinct epidemiological studies have often been directly compared without considering the analysis conditions. To address these issues, we first quantitatively evaluated the effects of analysis conditions on risk estimation for radiation-induced solid cancers in comparative epidemiological studies. “Apparent risks” dependent on age and follow-up periods were estimated in a virtual Japanese population with “a net risk” using the Life Span Study data. The estimated cancer risks were affected by the exposed and attained ages, length of follow-up period, age at the start of follow-up, and estimation methodologies for excess relative risks. These apparent risks differed by a maximum of approximately 5 times; thus, it greatly impacts the discussion of the dose-rate effectiveness factor. We estimated the excess relative risks under three basic scenarios corresponding to accidental release, occupational, and lifelong exposure for this virtual population. Considering that the initial age at exposure remained unchanged, the estimated risks of the 10-year exponential decline exposure and acute exposure were almost the same. The estimated risk of chronic exposure was lower than that of acute exposure, without considering the biological effects of dose and dose-rate.