Risk coefficient for γ-rays with regard to solid cancer

A previous investigation has uncoupled the solid cancer risk coefficient for neutrons from the low dose estimates of the relative biological effectiveness (RBE) of neutrons and the photon risk coeffi-cient, and has related it to two more tangible quantities, the excess relative risk (ERR1) due to an in-termediate reference dose D1=1 Gy of γ-rays and the RBE of neutrons, R1, against this reference dose. With tentatively assumed RBE values between 20 and 50 and in terms of organ-averaged doses – rather than the usually invoked colon doses – the neutron risk factor was seen to be in general agree-ment with the current risk estimate of the International Commission on Radiation Protection, ICRP. The present assessment of the risk coefficient for γ-rays incorporates – in terms of the unchanged A-bomb dosimetry system, DS86 – this treatment of the neutrons, but is, otherwise, largely analogous to the evaluation of the A-bomb data for the ICRP report and for the recent report of the United Nations Scientific Committee on the effects of ionizing radiation, UNSCEAR. The resulting central estimate of the lifetime attributable risk (LAR) for solid cancer mortality is for a working population (ages 25 to 65) 0.043/Gy, nearly the same whether the age at exposure or the attained age model is used for risk projection. For a population of all ages 0.042/Gy is obtained with the attained age model and 0.068/Gy with the age at exposure model. The values do not include a dose and dose rate effectiveness factor