Protracted exposure to low-dose ionising radiation and cancer incidence among Canadian nuclear power plant workers

Ionising radiation is a human carcinogen; however, there are uncertainties about the shape of the exposure-response function at low doses. We evaluated the relationship between radiation dose and cancer incidence in a cohort of Canadian nuclear power plant workers (NPPWs) with protracted exposures to low-dose ionising radiation.

The cohort included 75 350 workers employed at one of five Canadian nuclear power plants any time between 1945 and 2010. Exposure to cumulative whole-body effective dose was determined through personal monitoring. A total of 4370 incident cancers were identified through record linkage of these workers to national cancer registries (1969-2010). Vital status was determined through linkages to national mortality and tax databases. Standardised incidence ratios (SIRs) were calculated to compare cancer incidence rates of the cohort with the Canadian general population. Poisson regression was used to characterise dose-response relationships via categorical and linear excess relative risk (ERR) models.

Significantly elevated SIRs were found for solid cancers (combined), melanoma, colon and prostate cancer, while a reduced SIR was found for lung cancer. Positive, but not statistically significant excess risks were found for melanoma (ERR/100 mSv=0.32; 95% CI: -0.23 to 0.87) and prostate cancer (ERR/100 mSv=0.12; 95% CI: -0.05 to 0.29). An inverse association was found for lung cancer (ERR/100 mSv=-0.18; 95% CI: -0.01 to -0.36).

Our findings suggest that Canadian NPPWs have increased risks of prostate cancer and melanoma from low-dose ionising radiation exposure. Estimates should be cautiously interpreted due to the inability to adjust for demographic and lifestyle factors.