Objective To evaluate the effect of protracted low dose, low dose rate exposure to ionising radiation on the risk of cancer.
Design Multinational cohort study.
Setting Cohorts of workers in the nuclear industry in France, the UK, and the US included in a major update to the International Nuclear Workers Study (INWORKS).
Participants 309 932 workers with individual monitoring data for external exposure to ionising radiation and a total follow-up of 10.7 million person years.
Main outcome measures Estimates of excess relative rate per gray (Gy) of radiation dose for mortality from cancer.
Results The study included 103 553 deaths, of which 28 089 were due to solid cancers. The estimated rate of mortality due to solid cancer increased with cumulative dose by 52% (90% confidence interval 27% to 77%) per Gy, lagged by 10 years. Restricting the analysis to the low cumulative dose range (0-100 mGy) approximately doubled the estimate of association (and increased the width of its co