Time variations in radiation-induced relative risk and implications for population cancer risks

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Abstract
The Japanese bomb survivors and 12 other cohorts have been analysed and provide evidence for a reduction in the radiation-induced relative risk of cancers (other than leukaemia) with time following exposure. For the youngest age groups excess relative risk varies in proportion to (time since exposure)-j for j between 0.6 and 3.1. This is equivalent to an annual reduction of 4.1-9.4% in excess relative risk (depending on the year after which this reduction is assumed to take effect). For the older age groups there is little evidence for such a reduction in relative risk with time; indeed there are indications that in this group relative risk might increase with time after exposure. There are indications from the Japanese data that the absolute risk model (with time after exposure adjustment) might fit better than the time-adjusted relative risk model.