Solid cancer mortality associated with chronic external radiation exposure at the French atomic energy commission and nuclear fuel company

Our plain-English summary of Solid cancer mortality associated with chronic external radiation exposure at the French atomic energy commission and nuclear fuel company, by C. Metz-Flamant, E. Samson, S. Caër-Lorho, et al (Radiation Research, 2011).

The study

• Authors: C. Metz-Flamant, E. Samson, S. Caër-Lorho, A. Acker, D. Laurier
• Journal: Radiation Research
• Published: 2011;176(1):115-27
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Studies of nuclear workers make it possible to directly quantify the risks associated with ionizing radiation exposure at low doses and low dose rates. Studies of the CEA (Commissariat à l'Energie Atomique) and AREVA Nuclear Cycle (AREVA NC) cohort, currently the most informative such group in France, describe the long-term risk to nuclear workers associated with external exposure. Our aim is to assess the risk of mortality from solid cancers among CEA and AREVA NC nuclear workers and its association with external radiation exposure. Standardized mortality ratios (SMRs) were calculated and internal Poisson regressions were conducted, controlling for the main confounding factors [sex, attained age, calendar period, company and socioeconomic status (SES)]. During the period 1968-2004, there were 2,035 solid cancers among the 36,769 CEA-AREVA NC workers. Cumulative external radiation exposure was assessed for the period 1950-2004, and the mean cumulative dose was 12.1 mSv. Mortality rates for all causes and all solid cancers were both significantly lower in this cohort than in the general population. A significant excess of deaths from pleural cancer, not associated with cumulative external dose, was observed, probably due to past asbestos exposure. We observed a significant excess of melanoma, also unassociated with dose. Although cumulative external dose was not associated with mortality from all solid cancers, the central estimated excess relative risk (ERR) per Sv of 0.46 for solid cancer mortality was higher than the 0.26 calculated for male Hiroshima and Nagasaki A-bomb survivors 50 years or older and exposed at the age of 30 years or older. The modification of our results after stratification for SES demonstrates the importance of this characteristic in occupational studies, because it makes it possible to take class-based lifestyle differences into account, at least partly. These results show the great potential of a further joint international study of nuclear workers, which should improve knowledge about the risks associated with chronic low doses and provide useful risk estimates for radiation protection.

In plain English

This cohort study followed 36,769 French nuclear workers. All were employed for more than a year between 1950 and 1994 by the French atomic energy commission (CEA) or the nuclear fuel company AREVA NC, and all were monitored for external radiation. Deaths were tracked from 1968 to 2004. The average recorded cumulative radiation dose across the cohort was 12.1 mSv. There were 5,443 deaths, 2,035 of them from solid cancers. Compared with the French general population, the workers had lower death rates overall and from solid cancers. Pleural cancer deaths were higher than expected: 36 deaths, giving a standardized mortality ratio of 1.67 (95% confidence interval 1.17 to 2.32). This excess appeared only among workers hired before 1970 and was not associated with radiation dose. The authors linked it to past asbestos exposure at CEA, but they did not analyze individual asbestos exposure. Melanoma deaths were also in excess and also not linked to dose. Radiation dose was not significantly associated with death from all solid cancers. The authors noted limited statistical power and a lack of individual smoking data.

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: Cohort study of nuclear workers. Death rates were compared with the French general population (standardized mortality ratios), and an internal analysis related deaths to cumulative external radiation dose using Poisson regression.
• Who was studied: 36,769 permanent workers employed more than 1 year between 1950 and 1994 by CEA or AREVA NC in France and monitored for external radiation. Deaths were followed from 1968 through 2004. 81.8% were men. Workers at CEA military research sites and uranium miners were excluded.
• Exposure: External ionizing radiation (mainly X rays and gamma rays) recorded by personal dosimeters. Neutron doses were not included. Mean cumulative dose was 12.1 mSv in the whole cohort and 21.5 mSv among the 56% of workers with at least one measurable exposure. The maximum was 554.6 mSv. Asbestos exposure was not measured; the authors discussed it only as the likely explanation for the pleural cancer excess.
• Main results:
  • Compared with the French general population, the whole cohort had lower mortality from all causes (SMR 0.64, 95% CI 0.62 to 0.66) and from all solid cancers (SMR 0.70, 95% CI 0.67 to 0.74).
  • Pleural cancer deaths in the cohort were significantly higher than in the French population: 36 observed deaths, SMR 1.67 (95% CI 1.17 to 2.32).
  • The pleural cancer excess was seen only among workers hired before 1970, although the test for differences between hiring periods was not statistically significant.
  • Pleural cancer was not associated with cumulative radiation dose.
  • The authors linked the pleural cancer excess among workers hired before 1970 to past asbestos exposure at CEA, with a delay of about 30 to 40 years between exposure and onset.
  • Melanoma deaths were significantly in excess compared with the French population (39 deaths, SMR 1.64, 95% CI 1.17 to 2.24). The excess was not associated with cumulative dose.
  • For all solid cancers, the excess relative risk per sievert was 0.46 (90% CI minus 0.48 to 1.54). It was positive but not significantly different from zero.
  • For lung cancer, the excess relative risk per sievert was 0.94 (90% CI minus 0.83 to 3.25). It was positive but not significantly different from zero.
  • When the analysis was not adjusted for socioeconomic status, the dose-related risk estimates rose substantially and became statistically significant.
• The authors' conclusion: The authors concluded that they found no significant association between radiation dose and death from solid cancers in this enlarged cohort with longer follow-up. Their central risk estimate was higher than that for Hiroshima and Nagasaki atomic bomb survivors, but its confidence interval was consistent with both that estimate and one half its size.
• Limitations the authors state:
  • Lack of statistical power, leading to wide confidence intervals.
  • No individual smoking data, so confounding by smoking could not be ruled out.
  • Follow-up began only in 1968, so 158 workers who died before then were excluded.
  • Doses below the dosimeter detection limit were counted as zero; about 46% of workers received only such doses.
  • Neutron doses were not included because of sparse data and substantial uncertainty.
  • Individual internal contamination results were not yet available for each cohort member. Such data, together with data on carcinogens such as asbestos, had only recently been collected for workers at Pierrelatte.

Topics

Medical terms in this study, explained in our Lexicon: Atomic Energy Commission, standardized mortality ratio (SMR), Confounding, Cumulative Dose, Asbestos Exposure, Relative Risk.

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• Impact of chemical exposure on cancer mortality in a French cohort of uranium processing workers — S. Zhivin, D. Laurier, et al. (2013)
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• Mortality and cancer incidence of Australian participants in the British nuclear tests in Australia — R.T. Gun, J. Parsons, et al. (2008)

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