Risk of cancer from occupational exposure to ionising radiation: retrospective cohort study of workers in France, the United Kingdom, and the United States (INWORKS)

Our plain-English summary of Risk of cancer from occupational exposure to ionising radiation: retrospective cohort study of workers in France, the United Kingdom, and the United States (INWORKS), by D.B. Richardson, E. Cardis, R.D. Daniels, et al (BMJ, 2015).

The study

• Authors: D.B. Richardson, E. Cardis, R.D. Daniels, M. Gillies, J.A. O'Hagan, G.B. Hamra, R. Haylock, D. Laurier, K. Leuraud, M. Moissonnier, M.K. Schubauer-Berigan, I. Thierry-Chef, A. Kesminiene
• Journal: BMJ
• Published: 2015;351:h5359
• Cited by: 258 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Study Question: Is protracted exposure to low doses of ionising radiation associated with an increased risk of solid cancer?

Methods: In this cohort study, 308,297 workers in the nuclear industry from France, the United Kingdom, and the United States with detailed monitoring data for external exposure to ionising radiation were linked to death registries. Excess relative rate per Gy of radiation dose for mortality from cancer was estimated. Follow-up encompassed 8.2 million person years. Of 66,632 known deaths by the end of follow-up, 17,957 were due to solid cancers.

Study Answer And Limitations: Results suggest a linear increase in the rate of cancer with increasing radiation exposure. The average cumulative colon dose estimated among exposed workers was 20.9 mGy (median 4.1 mGy). The estimated rate of mortality from all cancers excluding leukaemia increased with cumulative dose by 48% per Gy (90% confidence interval 20% to 79%), lagged by 10 years. Similar associations were seen for mortality from all solid cancers (47% (18% to 79%)), and within each country. The estimated association over the dose range of 0-100 mGy was similar in magnitude to that obtained over the entire dose range but less precise. Smoking and occupational asbestos exposure are potential confounders; however, exclusion of deaths from lung cancer and pleural cancer did not affect the estimated association. Despite substantial efforts to characterise the performance of the radiation dosimeters used, the possibility of measurement error remains.

What This Study Adds: The study provides a direct estimate of the association between protracted low dose exposure to ionising radiation and solid cancer mortality. Although high dose rate exposures are thought to be more dangerous than low dose rate exposures, the risk per unit of radiation dose for cancer among radiation workers was similar to estimates derived from studies of Japanese atomic bomb survivors. Quantifying the cancer risks associated with protracted radiation exposures can help strengthen the foundation for radiation protection standards.

Funding, Competing Interests, Data Sharing: Support from the US Centers for Disease Control and Prevention; Ministry of Health, Labour and Welfare of Japan; Institut de Radioprotection et de Sûreté Nucléaire; AREVA; Electricité de France; US National Institute for Occupational Safety and Health; US Department of Energy; and Public Health England. Data are maintained and kept at the International Agency for Research on Cancer.

© Richardson et al 2015.

In plain English

This retrospective cohort study (INWORKS) pooled 308,297 nuclear workers from France, the UK and the USA. All were monitored with personal dosimeters for external ionising radiation and linked to death records; follow-up ran between 1944 and 2005. Asbestos exposure was not measured; it appeared only as a possible distorting factor. Among the 257,166 workers with a positive recorded dose, the mean estimated cumulative colon dose was 20.9 mGy (median 4.1 mGy). Of 66,632 deaths, 19,748 were from cancer. For doses received at least 10 years earlier, the relative death rate from cancers other than leukaemia rose an estimated 48% per gray (90% confidence interval 20% to 79%), and for solid cancers 47% per gray (18% to 79%). To address possible bias from smoking and occupational asbestos exposure, the authors repeated the analysis without lung and pleural cancers. The estimate was similar: an excess relative rate of 0.43 per gray (0.08 to 0.82). The authors concluded that their results provide evidence of a linear increase in cancer death rates with dose at low dose rates. They noted possible dose measurement errors and unmeasured smoking.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: retrospective cohort study (pooled analysis of nuclear worker cohorts, Poisson regression)
• Who was studied: 308,297 nuclear industry workers in France (followed 1968-2004), the UK (1946-2001) and the USA (1944-2005). All were employed for at least one year and monitored with personal dosimeters; 87% were men. Follow-up totalled 8.2 million person years.
• Exposure: External exposure to ionising radiation (photons), expressed as estimated cumulative dose to the colon and lagged by 10 years. Among the 257,166 workers with a positive recorded dose: median 4.1 mGy, mean 20.9 mGy, maximum 1331.7 mGy. Asbestos exposure was not measured or directly adjusted for.
• Main results:
  • Of 66,632 deaths in the whole cohort, 19,748 were due to cancer
  • The estimated rate of death from all cancers excluding leukaemia increased by 48% per Gy of cumulative dose (90% CI 20% to 79%), lagged 10 years. The increase for solid cancers was 47% per Gy (18% to 79%).
  • Excess relative rate per Gy (90% CI): 0.48 (0.20 to 0.79) for all cancers other than leukaemia; 0.47 (0.18 to 0.79) for solid cancers
  • Excluding lung cancer (to address smoking), the excess relative rate for solid cancers was 0.46 per Gy (0.11 to 0.85)
  • Excluding lung and pleural cancer (to address possible bias from asbestos exposure), the excess relative rate for the remaining solid cancers was 0.43 per Gy (0.08 to 0.82). This was similar to the estimate for all solid cancers.
  • Restricted to cumulative doses of 0-100 mGy, the excess relative rate for cancer other than leukaemia was 0.81 per Gy (90% CI 0.01 to 1.64). This was less precise than the full-range estimate.
  • About 209 of the 19,064 deaths from cancer other than leukaemia were estimated to be excess deaths associated with external radiation exposure
  • No evidence that the association differed between the three countries
• The authors' conclusion: The authors concluded that the study provides evidence of a linear increase in the excess relative rate of cancer mortality with increasing radiation exposure at the low dose rates typical of the nuclear industry. They also concluded that the risk per unit dose was similar to estimates from Japanese atomic bomb survivors.
• Limitations the authors state:
  • Errors in measuring radiation exposure, especially in early years
  • Some radiation exposures may not appear in the available records
  • Smoking was not measured
  • Smoking and occupational asbestos exposure are potential confounders that could not be adjusted for directly
  • Possible residual confounding by socioeconomic status, which was based on job title

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Cohort Study, Cumulative Exposure, confidence interval, Asbestos Exposure, Lung Cancer.

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