Mesothelioma mortality within two radiation monitored occupational cohorts

Abstract

Purpose

The risk of mesothelioma, including cancers of the pleura and peritoneum, was examined within two large cohorts of workers monitored for exposure to ionizing radiation.

Methods and materials

Mortality was assessed among 253,632 workers routinely monitored for external radiation, including 30,724 industrial radiographers (IR) at shipyards, 142,583 workers at nuclear power plants (NPP), and 83,441 IR who had not worked at an NPP or shipyard. Follow-up was from 1969 through 2011. Standardized mortality ratios (SMRs) and 95% confidence intervals (CIs) were computed; observed numbers of deaths from mesothelioma (including cancers of the pleura and peritoneum) and asbestosis were compared with numbers expected based on age-, sex-, and calendar year-specific national mortality rates. Job history and quantitative asbestos exposure data were unavailable, but work at a shipyard was taken as a surrogate for the likelihood of exposure. Cox proportional hazards models were used to estimate hazard ratios (HRs) for mesothelioma in relation to estimated cumulative radiation exposure to the lung.

Results

The mean duration of follow-up was 25.3 years (max 42 years). The mean cumulative lung dose was 28.6 mGy (7.3% > 250 mGy). Nearly 20% of the workers had died by 2011. A total of 421 mesothelioma deaths were found (75% occurring after 1999) with increased SMRs among workers monitored in shipyards (SMR 9.97; 95% CI 8.50–11.63) and for NPP workers (SMR 5.55; 95% CI 4.88–6.29), but not for IR who had not worked in shipyards (SMR 1.15; 95% CI 0.53–2.19). Likewise, deaths from asbestosis (n = 189) were also increased for shipyard and NPP workers (SMR = 18.1 and 9.2, respectively), but not among workers who never worked at a shipyard or NPP (SMR = 0.70; n = 1). Radiation dose to the lung was not associated with a statistically meaningful dose-response trend for mesothelioma in the combined cohorts (HR at 100 mGy = 1.10; 95% CI 0.96–1.27; p = .18), nor was mesothelioma risk associated with radiation exposure among IR who had not worked in a shipyard and assumed minimally exposed to asbestos.

Conclusions

An elevated rate of death from mesothelioma was observed in two radiation-exposed occupational groups with potential for asbestos exposure. The increased risk of death from asbestosis, combined with little evidence of a rising trend in mesothelioma mortality with increasing radiation exposure, suggests that the mesothelioma (and asbestosis) excess in these workers was due to asbestos exposure in shipyards and power plants and not to occupational low-dose radiation.

Keywords:

• Mesothelioma
• asbestos
• cohort
• epidemiology

Disclosure statement

M. T. Mumma and W. J. Blot have previously consulted with a former manufacturer of products containing asbestos on matters related to litigation. Other authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported in part by a grant from the U.S. Nuclear Regulatory Commission [NRC-HQ‐60‐14‐G‐0011], a grant from the Centers for Disease Control and Prevention [5UE1EH000989], a grant from the National Aeronautics and Space Administration [Grant No. NNX15AU88G], and grants from the U.S. Department of Energy [Grant No. DE-SC0008944 and Grant No. DE-AU0000042 awarded to the National Council on Radiation Protection and Measurements, which included interagency support from the U.S. Nuclear Regulatory Commission, the U.S. Environmental Protection Agency, and the National Aeronautics and Space Administration]. Furthermore, contract support was received by Oak Ridge National Laboratory from the Office of Radiation and Indoor Air, U.S. Environmental Protection Agency, under Interagency Agreement DOE No. 1824 S581‐A1, under contract No. DE-AC05‐00OR22725 with UT-Battelle; and contract support was received by Oak Ridge Associated Universities from the U.S. Department of Energy under contract No. DE-SC0014664.

Notes on contributors

Michael T. Mumma

Michael T. Mumma is the Director of Information Technology at the International Epidemiology Institute and the International Epidemiology Field Station for Vanderbilt University Medical Center. He has over 20 years of experience in data analysis and conducting epidemiologic investigations.

Jennifer L. Sirko

Jennifer L. Sirko is an epidemiologist with over 10 years of experience in occupational and public health research. In addition to her work with the International Epidemiology Institute, she is currently a research officer with the Pew Charitable Trusts.

John D. Boice

John D. Boice is a radioepidemiologist with over 40 years of experience. He is the President of the National Council on Radiation Protection and Measurements and a professor of medicine at Vanderbilt University. He is the recipient of the E.O. Lawrence award from the Department of Energy. Dr. Boice is the creator and leader of the Million Person Study in the United States.

William J. Blot

William J. Blot is professor of medicine at Vanderbilt University School of Medicine and chief executive officer of the International Epidemiology Institute. Prior to co-founding IEI in 1994, he directed research into the causes of cancer for 20 years at the National Cancer Institute. He currently directs the NIH-funded Southern Community Cohort Study, one of the largest epidemiologic studies yet undertaken to assess reasons for racial disparities in cancer incidence and mortality.