Purpose of the Study
The study examined whether long-term, low-level occupational exposure to ionising radiation is associated with an increased risk of developing cancer among Canadian NPPWs. While high-dose radiation is a known carcinogen, there is ongoing scientific uncertainty about cancer risks at low doses received over many years, which is typical in nuclear workplaces. This research helps address that gap.
What Is Meant by “Low-Dose” Radiation
In this study, low-dose ionising radiation refers to cumulative whole-body radiation doses accumulated slowly over a working lifetime, rather than from short-term or accidental high-dose exposures.
- Risk estimates are expressed per 10 rem (10,000 mrem) of cumulative dose.
- Workers with more than 50 rem (50,000 mrem) of lifetime exposure were excluded from internal dose–response analyses to ensure the study focused on low-dose occupational exposure.
The average cumulative lifetime dose in the cohort was approximately 1,200 mrem total. For context, a typical Canadian nuclear power plant worker today receives approximately 100 mrem per year from occupational exposure.
Study Population and Methods
The cohort included 75,350 workers employed at one of five Canadian nuclear power plants (Pickering, Darlington, Bruce, Point Lepreau, and Gentilly) between 1945 and 2010.
Workers were followed for cancer incidence between 1969 and 2010, using national cancer registries.
Researchers identified 4,370 new (incident) cancer cases during follow-up.
Cancer rates among workers were compared to the general Canadian population, and internal analyses examined whether cancer risk increased with increasing radiation dose.
Key Findings
Overall Cancer Risk
Nuclear power plant workers had a slightly higher overall incidence of solid cancers compared with the general Canadian population.
Specific Cancers with Elevated Incidence
Prostate cancer and melanoma (skin cancer) were consistently higher than expected with prostate cancer ~27% higher and melanoma approximately 31% higher when compared to the general Canadian population.
Colon cancer incidence was also modestly elevated at rate of ~15% higher when compared to the general Canadian population.
All solid cancers (meaning all non-blood cancers combined, such as cancers of organs and tissues) were ~8% higher when compared to the general Canadian population.
Lung cancer incidence was lower than in the general population (~9% lower), likely reflecting differences in smoking patterns rather than radiation effects.
An important note that the increase cancer rates are relative increases on top of an already common baseline, and they don’t mean a large increase in absolute risk for any one worker. For example, in the general Canadian population, about 11–13% of men (roughly 1 in 8 to 1 in 9) will be diagnosed with prostate cancer over their lifetime. If an occupational group experiences a 27% higher incidence rate, this would translate to an estimated lifetime risk of roughly 14–16% (about 1 in 6 to 1 in 7 men). This does not mean radiation exposure causes prostate cancer in most workers, nor does it mean an individual worker has a 27% chance of developing cancer. The increase represents a modest absolute change on top of an already common cancer.
Dose–Response Results
When comparing workers with different radiation doses, positive (but not statistically definitive) dose–response trends were observed for:
- Prostate cancer
- Melanoma
The study found that for every additional 10 rem (10,000 mrem) of radiation a worker accumulates over their career, their chance of developing prostate cancer increases by approximately 12% and melanoma increases by approximately 30%.
These findings suggest a possible association between increasing cumulative radiation dose and cancer risk, but results should be interpreted cautiously due to statistical uncertainty and potential confounding factors.
Important Limitations
The study could not adjust for lifestyle factors such as smoking, sun exposure, or cancer screening practices.
Increased prostate cancer detection may partly reflect more frequent medical screening among workers (a known occupational study issue).
Most workers were male, limiting analysis of some female-specific cancers.
Why This Matters
The study reinforces that even low-dose, long-term radiation exposure warrants continued vigilance. While risks are not considered large, they are relevant over full working careers and across a large workforce.
Employers should:
- Communicate the results of the study to workers, retirees and the JHSCs
- While regulatory dose limits are being met, reconfirm that ALARA remains the operational standard
Enhance occupational health surveillance and education around prostate cancer and skin cancer