Occupational radiation exposure and cause-specific mortality in a cohort of Canadian medical workers

The health effects of high and moderate doses of ionizing radiation are recognized, but the impacts at lower doses are less clear. Medical workers represent the largest occupational group exposed to radiation. Herein, we examine mortality patterns in a Canadian cohort of medical workers, sex differences in risk, and trends in exposure over time.

Annual whole-body effective doses for 301,740 medical workers between 1951 and 2018 were obtained from the Canadian National Dose Registry. Dose trends were characterised by job class and sex. Underlying cause of death was ascertained using linkage to mortality data through 2020. Standardized mortality ratios (SMRs) were estimated to compared the risk of mortality among 124,180 workers with with a lifetime cumulative dose > 0 mSv to the Canadian general population. Internal cohort comparisons incorporated person-time and events among unexposed workers. Poisson regression was used for internal cohort comparisons to explore healthy worker bias.

The mean annual radiation dose among workers declined from 0.56 mSv during 1948-1977 to 0.09 mSv in 2000-2018. Compared to the general Canadian population, all-cause mortality was lower for both men (SMR = 0.54, 95% CI: 0.52-0.55) and women (SMR = 0.57, 95% CI: 0.55-0.59). No elevated cause-specific mortality risks were observed. Internal cohort analyses suggests that the healthy worker effects may be contributing to lower mortality rates in workers exposed to low doses of radiation.

Consistent with earlier studies, radiation-exposed medical workers have reduced mortality relative to the general population, likely reflecting a healthy worker effect.