Mesothelioma mortality within two radiation monitored occupational cohorts

Our plain-English summary of Mesothelioma mortality within two radiation monitored occupational cohorts, by M.T. Mumma, J.L. Sirko, J.D. Boice, et al (International Journal of Radiation Biology, 2022).

The study

• Authors: M.T. Mumma, J.L. Sirko, J.D. Boice, W.J. Blot
• Journal: International Journal of Radiation Biology
• Published: 2022;98(4):786-794
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

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.

In plain English

This study followed 253,632 US radiation-monitored workers (industrial radiographers and nuclear power plant workers) for deaths from 1969 through 2011. No asbestos measurements were available. The authors treated ever being monitored at a shipyard, naval facility or nuclear power plant as a sign of likely asbestos exposure. Deaths were compared with US national rates using standardized mortality ratios (SMRs). There were 421 mesothelioma deaths and 189 asbestosis deaths. Before 1999, mesothelioma was counted as cancers of the pleura and peritoneum. The mesothelioma SMR was 9.97 (95% CI 8.50–11.63) among workers ever monitored at shipyards and 5.55 (95% CI 4.88–6.29) among those monitored only at nuclear power plants. It was 1.15 (95% CI 0.53–2.19), not significantly raised, among 83,441 radiographers who worked at neither (9 deaths). Asbestosis showed the same pattern. Cumulative lung radiation dose showed no statistically significant trend with mesothelioma. The authors suggested the excess was due to asbestos in shipyards and power plants, not low-dose radiation. They noted they lacked individual asbestos and smoking data and could not discount residual confounding by asbestos.

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 mortality study. Death rates were compared with US national rates (standardized mortality ratios), plus internal Cox proportional hazards analyses of cumulative radiation dose to the lung.
• Who was studied: 253,632 US workers drawn from the Million Person Study: nuclear power plant (NPP) workers monitored at an NPP between 1969 and 1984 (a 10% random sample of those with career badge dose under 10 mSv, plus all above 10 mSv) and industrial radiographers (IR). The groups were 30,724 ever monitored at a shipyard (27,608 shipyard only plus 3,116 at both a shipyard and an NPP), 139,467 monitored only at an NPP, and 83,441 IR never monitored at a shipyard or NPP. Mortality follow-up ran from 1969 through 2011, and 93.2% of the workers were male.
• Exposure: Asbestos exposure was not measured and no fiber types were named. Possible asbestos exposure was inferred from ever being monitored for radiation at a shipyard, marina, dry dock or naval facility, or at an NPP. Radiation exposure was external gamma radiation, converted to cumulative lung dose (mean 28.6 mGy; mean career badge dose 35.4 mSv).
• Main results:
  • Whole cohort: 421 mesothelioma deaths, SMR 6.10 (95% CI 5.53–6.71). All mesothelioma deaths were among men.
  • Whole cohort: 189 asbestosis deaths (SMR 11.4; 95% CI 9.85–13.2), all among men according to the text.
  • Workers ever monitored at a shipyard: 163 mesothelioma deaths, SMR 9.97. The 95% CI is 8.50–11.63 in the abstract and 8.50–11.6 in Table 2. Same group: 100 asbestosis deaths, SMR 18.1 (95% CI 14.8–22.1).
  • Workers monitored only at NPPs: 249 mesothelioma deaths, SMR 5.55 (95% CI 4.88–6.29). Same group: 88 asbestosis deaths, SMR 9.16 (the table gives 95% CI 7.35–11.3).
  • IR never monitored at a shipyard or NPP: 9 mesothelioma deaths, SMR 1.15 (95% CI 0.53–2.19), not significantly raised. Same group: 1 asbestosis death, SMR 0.70 (95% CI 0.01–3.89).
  • Mesothelioma rates stayed raised late in follow-up. In 2000–2011 there were 315 mesothelioma deaths (75% of all), SMR 5.85 (95% CI 5.22–6.53). For 30 or more years since first monitoring, the SMR was 8.12 (95% CI 7.13–9.21; 241 deaths).
  • Internal analysis of 157,855 workers, with the first 10 years of follow-up excluded and doses lagged 10 years. No lung-dose category was significantly elevated compared with 1 to under 10 mGy. The hazard ratio at 100 mGy was 1.10 (95% CI 0.96–1.27; p = .18 for trend).
  • Among the 83,441 IR not known to have worked in shipyards, the test for a linear trend with lung dose was not significant (p = .56). This was based on only nine mesothelioma deaths.
• The authors' conclusion: The authors stated that their findings suggest the excess of mesothelioma and asbestosis deaths in these workers was due to asbestos exposure in shipyards and power plants, not to occupational low-dose radiation. They also reported that low-dose radiation in these settings was not found to be associated with mesothelioma.
• Limitations the authors state:
  • The authors could not estimate asbestos exposure for individual workers. They had no job titles or other data to quantify it.
  • Residual confounding by asbestos in the radiation dose-response analyses could not be discounted.
  • The study assumed that cancers of the pleura and peritoneum (used before ICD-10) were mainly mesotheliomas.
  • Pre-ICD-10 death codes for pleural and peritoneal cancer likely undercount mesothelioma deaths.
  • There were no smoking data, and few female workers.
  • Too few mesothelioma deaths (nine) among IR who never worked in shipyards prevented informative dose analyses in that group.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleura, Peritoneum, standardized mortality ratio (SMR), confidence interval, Asbestos Exposure, Hazard Ratio, Dose-response relationship.

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