The risk of non-melanoma skin cancer incidence in the Japanese atomic bomb survivors

The latest Japanese atomic bomb survivor non-melanoma skin cancer incidence dataset is analysed and indicates substantial curvilinearity in the dose-response curve, consistent with a possible dose threshold of about 1 Sv, or with a dose-response in which the excess relative risk is proportional to the fourth power of dose, with a turning-over in the dose-response at high doses (> 3 Sv). The time distribution of the radiation-induced excess risk is best described by a model in which the relative excess risk is proportional to a product of powers of time since exposure and attained age. The fits of generalized relative risk models with exponential functions of time and age at exposure (and in particular of attained age) to adjust the relative risk are less satisfactory, as also are the fits of other models in which products of powers of time since exposure, age at exposure and attained age adjust the excess absolute risk. Sensitivity analyses indicate the importance of likely adjustments to the Hiroshima neutron doses for the optimal model parameters, particularly if values of the neutron relative biological effectiveness (RBE) of more than 5 are assumed. If adjustments recently proposed are made to the Hiroshima neutron doses, then using the optimal model (in which excess risk is proportional to the fourth power of dose) the best estimate of the neutron RBE is 1.3 (95% CI < 07.1). However, uncertainties in skin dose estimates for the atomic bomb survivors means that the findings with respect to the neutron RBE and the non-linearity in the dose-response curve should be treated with caution.