Effect of age-related baseline risk on radiation dose response for coronary heart disease

We attempted to estimate the mortality risk of radiation-associated coronary heart disease (CHD) by using a model in which radiation was assumed to participate in the atherosclerotic process jointly with ageing. Model parameters were determined by fitting the Life Span Study data of atomic bomb survivors. According to the model, the excess relative risk (ERR) varies depending on the baseline risk; when applied to the death statistics of Japan and the USA, the estimated ERR was consistently higher in the Japanese population. The absolute risk showed an opposite trend, such that the estimated lifetime attributable risk was approximately two times higher in the US population. Excess cases were expected to appear in old age almost synchronously with spontaneous cases; in contrast, the risk is practically unnoticeable for those young to middle aged. Our model suggests that the radiation dose-response curve for CHD, as well as the latency in epidemiological studies, could be modified by the baseline risk.