A nested case-control study of lung cancer risk and ionizing radiation exposure at the portsmouth naval shipyard

Our plain-English summary of A nested case-control study of lung cancer risk and ionizing radiation exposure at the portsmouth naval shipyard, by J.H. Yiin, S.R. Silver, R.D. Daniels, et al (Radiation Research, 2007).

The study

• Authors: J.H. Yiin, S.R. Silver, R.D. Daniels, D.D. Zaebst, E.A. Seel, T.L. Kubale
• Journal: Radiation Research
• Published: 2007;168(3):341-8
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Results have been inconsistent between studies of lung cancer risk and ionizing radiation exposures among workers at the Portsmouth Naval Shipyard (PNS). The purpose of this nested case-control study was to evaluate the relationship between lung cancer risk and external ionizing radiation exposure while adjusting for potential confounders that included gender, radiation monitoring status, smoking habit surrogates (socioeconomic status and birth cohort), welding fumes and asbestos. By incidence density sampling, we age-matched 3,291 controls selected from a cohort of 37,853 civilian workers employed at PNS between 1952 and 1992 with 1,097 lung cancer deaths from among the same cohort. Analyses using conditional logistic regression were conducted in various model forms: log-linear (main), linear excess relative risk (ERR), and categorical. Lung cancer risk was positively associated with occupational dose (OR = 1.02 at 10 mSv; 95% CI 0.99- 1.04) but flattened after the inclusion of work-related medical X-ray doses (OR = 1.00; 95% CI 0.98-1.03) in multivariate analyses. Similar risk estimates were observed in the linear ERR model at 10 mSv of cumulative exposure with a 15-year lag.

In plain English

This nested case-control study examined whether external ionizing radiation at work was linked to lung cancer deaths among civilian workers at the Portsmouth Naval Shipyard. From a cohort of 37,853 workers employed between 1952 and 1992, the authors compared 1,097 workers who died of lung cancer with 3,291 age-matched controls. They adjusted for gender, radiation monitoring status, socioeconomic status and birth cohort (used in place of smoking data, which were mostly missing), welding fumes and asbestos. An expert panel of industrial hygienists estimated the asbestos and welding fume exposures. Without adjustment, the odds ratio for lung cancer was 1.03 per 10 mSv of radiation dose (95% CI 1.00–1.05). After adjustment it was 1.02 (95% CI 0.99–1.04). When work-related medical X-ray doses were also added, it was 1.00 (95% CI 0.98–1.03). On its own, asbestos was associated with lung cancer (odds ratio 1.04 per 1,000 fiber-days/cm3, 95% CI 1.00–1.09). In the adjusted model this estimate fell to 1.02 (95% CI 0.98–1.07). The authors concluded that the radiation association remained positive but was not statistically significant after adjustment. They described their control for confounders as incomplete.

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: Nested case-control study within a cohort mortality study. Controls were chosen by incidence density sampling, three per case, and data were analysed with conditional logistic regression.
• Who was studied: Male and female civilian workers of all races employed at the Portsmouth Naval Shipyard (PNS) for at least 1 day between 1952 and 1992, with vital status followed through 1996. The study had 1,097 lung cancer deaths (cases) and 3,291 controls drawn from a cohort of 37,853 workers.
• Exposure: Cumulative external ionizing radiation dose to the lung (mSv, lagged 15 years), in some analyses with work-related medical X-ray doses added. Asbestos (fiber-days/cm3; no fiber type specified) and welding fume (mg-days/m3) were estimated from job, shop and time-period exposure matrices built by an expert panel, and were treated as potential confounders.
• Main results:
  • Without adjustment for confounders, lung cancer risk rose with occupational radiation dose: odds ratio 1.03 at 10 mSv (95% CI 1.00–1.05) in the log-linear model, and excess relative risk 3.6% per 10 mSv in the linear model.
  • In the unadjusted categorical analysis, compared with workers at 0–1 mSv, the odds ratio was 1.23 for 1–10 mSv and 1.54 (95% CI 1.14–2.07) for 10–50 mSv. It dropped to 1.21 in the highest dose category.
  • After adjusting for all potential confounders, the dose-response was weakly positive. The odds ratio was 1.02 at 10 mSv (95% CI 0.99–1.04) and the excess relative risk was 1.9% per 10 mSv. Categorical odds ratios were 1.17 (0.86–1.60) for 1–10 mSv, 1.45 (1.01–2.09) for 10–50 mSv and 1.13 (0.72–1.75) for the highest category, compared with the lowest dose group.
  • When work-related medical X-ray doses were added to occupational dose and all potential confounders were included, the odds ratio was 1.00 at 10 mSv (95% CI 0.98–1.03). The categorical model showed a decreasing trend (1.31, 1.03 and 0.95 across the three dose categories).
  • Mean cumulative asbestos exposure (15-year lag) was 456 fiber-days/cm3 in cases and 361 fiber-days/cm3 in controls.
  • Analysed on its own, lung cancer risk rose with asbestos exposure: odds ratio 1.04 at 1,000 fiber-days/cm3 (95% CI 1.00–1.09 in Table 5). All asbestos exposure categories had higher risk than the baseline, but the estimates decreased slightly as exposure categories increased.
  • In the multivariate model, the risk estimates for welding fume and asbestos were lower than when each was analysed on its own. For asbestos the estimate was 1.02 at 1,000 fiber-days/cm3 (95% CI 0.98–1.07).
  • In the multivariate model, women had lower lung cancer risk than men: risk estimate 0.42 (95% CI 0.28–0.60).
• The authors' conclusion: The authors concluded that birth cohort, socioeconomic status, welding fume and asbestos exposures, and occupational external ionizing radiation dose were positively associated with lung cancer mortality. In their view, the radiation association remained positive but was not statistically significant after adjusting for potential confounders. They described their control for confounders as incomplete, but it did attenuate the radiation risk estimates.
• Limitations the authors state:
  • Smoking data were almost unavailable for non-radiation workers. Socioeconomic status and birth cohort were used as surrogates, so some residual confounding or effect modification likely remains.
  • Usable air monitoring data for asbestos and welding fumes were scarce. Exposures therefore had to be estimated by an expert panel, and without monitoring data to validate those estimates, exposure misclassification remains possible.
  • Radiation dose estimates carry uncertainty, which the authors expected to be larger for medical X-ray doses.
  • Some relevant occupational radiation exposures likely remain undiscovered. Non-occupational medical and natural radiation sources were not evaluated.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Shipyards and maritime work.

Medical terms in this study, explained in our Lexicon: nested case-control study, Lung Cancer, Habit, Relative Risk, Cumulative Exposure.

Related studies

• Case-control study of lung cancer in civilian employees at the Portsmouth Naval Shipyard, Kittery, Maine — R.A. Rinsky, J.M. Melius, et al. (1988)
• Ionizing radiation: a risk factor for mesothelioma — J.E. Goodman, M.A. Nascarella, et al. (2009)
• Inter-rater agreement for a retrospective exposure assessment of asbestos, chromium, nickel and welding fumes in a study of lung cancer and ionizing radiation — E.A. Seel, D.D. Zaebst, et al. (2007)
• Cancer risks and low-level radiation in U.S. shipyard workers — G.M. Matanoski, J.A. Tonascia, et al. (2008)
• Risk of cancer from occupational exposure to ionising radiation: retrospective cohort study of workers in France, the United Kingdom, and the United States (INWORKS) — D.B. Richardson, E. Cardis, et al. (2015)
• Asbestos exposure control at Puget Sound Naval Shipyard — R.R. Beckett (1976)

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