Lung cancer and internal lung doses among plutonium workers at the Rocky Flats Plant: a case-control study

Our plain-English summary of Lung cancer and internal lung doses among plutonium workers at the Rocky Flats Plant: a case-control study, by S.C. Brown, M.F. Schonbeck, D. McClure, et al (American Journal of Epidemiology, 2004).

The study

• Authors: S.C. Brown, M.F. Schonbeck, D. McClure, A.E. Barón, W.C. Navidi, T. Byers, A.J. Ruttenber
• Journal: American Journal of Epidemiology
• Published: 2004;160(2):163-72
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The authors conducted a nested case-control study of the association between lung cancer mortality and cumulative internal lung doses among a cohort of workers employed at the Rocky Flats Plant in Colorado from 1951 to 1989. Cases (n = 180) were individually matched with controls (n = 720) on age, sex, and birth year. Annual doses to the lung from plutonium, americium, and uranium isotopes were calculated for each worker with an internal dosimetry model. Lung cancer risk was elevated among workers with cumulative internal lung doses of more than 400 mSv in several different analytical models. The dose-response relation was not consistent at high doses. Restricting analysis to those employed for 15-25 years produced a statistically significant linear trend with dose (chi-square = 67.2, p < 0.001), suggesting a strong healthy worker survivor effect. The association between age at first internal lung dose and lung cancer mortality was statistically significant (odds ratio = 1.05, 95% confidence interval: 1.01, 1.10). No associations were found between lung cancer mortality and cumulative external penetrating radiation dose or cumulative exposures to asbestos, beryllium, hexavalent chromium, or nickel.

In plain English

This nested case-control study examined lung cancer deaths among workers at the Rocky Flats nuclear weapons plant in Colorado. The authors compared 180 workers who died with lung cancer with 720 matched co-workers. They estimated each person's radiation dose to the lung from inhaled plutonium, americium and uranium. Exposures to asbestos, beryllium, hexavalent chromium and nickel came from a job exposure matrix. In the final models, lung cancer risk was statistically significantly raised in the group with more than 400 and up to 644 mSv when doses were lagged 10 or 15 years (odds ratio 2.71, 95% confidence interval 1.20 to 6.09, with a 10-year lag). Risk did not keep rising at higher doses. Among workers employed 15 to 25 years, risk rose with dose. Longer employment was linked to lower risk, which the authors said suggested a strong healthy worker survivor effect. Asbestos, the other three chemicals and external radiation were not significantly associated with lung cancer death, and the article shows no asbestos figures. Smoking did not change the dose findings by 10 percent or more.

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 of plutonium workers, analysed with conditional and ordinary logistic regression
• Who was studied: 180 lung cancer cases and 720 controls (4 per case, matched on sex and date of birth within 2.5 years). They were drawn from a database of 22,883 Rocky Flats Plant workers. Cases had worked at least 6 months between 1952 and 1989 and died before December 31, 1996. Only seven cases were women.
• Exposure: Main exposure: cumulative internal lung doses from plutonium isotopes, americium 241 and uranium isotopes, estimated with the CINDY dosimetry code. Also studied: external penetrating radiation dose, smoking, and annual exposures to asbestos, beryllium, hexavalent chromium and nickel estimated from a job exposure matrix.
• Main results:
  • In the final conditional model, odds ratios rose from the no-dose group to the group with more than 400 and up to 644 mSv, then fell for the two highest dose groups, when doses were lagged 10 or 15 years. In that group the odds ratio was 2.71 (95% CI 1.20, 6.09) with a 10-year lag and 3.32 (95% CI 1.50, 7.34) with a 15-year lag.
  • In the univariate model with a 10-year lag, no internal lung dose category was statistically significant.
  • Among workers employed 15 to 25 years, odds ratios rose with dose, reaching 5.04 (95% CI 1.55, 16.40) for more than 940 mSv, with a significant linear trend. Among workers employed less than 15 years or more than 25 years, odds ratios were mostly below one and none was significant.
  • Adjusting for the number of years with an above-zero lung dose doubled the odds ratios for doses above 100 mSv.
  • Among subjects who received internal lung doses, risk rose 5 percent per year of age at first internal lung dose (odds ratio 1.05, 95% CI 1.01, 1.10).
  • Longer employment was associated with lower lung cancer risk (odds ratio 0.97 per year, 95% CI 0.96, 0.99, univariate). The authors said this suggested a strong healthy-worker survivor effect.
  • Cumulative exposures to asbestos, beryllium, hexavalent chromium and nickel were not significantly associated with lung cancer mortality. The numbers were not shown.
  • Cumulative external penetrating radiation dose was not significantly associated with lung cancer.
  • Adding smoking (pack-years) to the models did not change the internal dose association by 10 percent or more.
• The authors' conclusion: The authors reported statistically significant lung cancer risks at cumulative internal lung doses above 400 mSv. They concluded that future studies of plutonium workers should include organ dose estimates based on the best available dosimetric models.
• Limitations the authors state:
  • The authors suggested the CINDY dosimetry code may have overestimated lung doses for subjects with high cumulative doses.
  • Smoking data were missing for 32 percent of cases and 16 percent of controls.
  • There were too few female cases to analyse men and women separately.
  • Asbestos and other chemical exposures had to be imputed for at least one year for most subjects. The authors reported that assigning zero exposure instead gave similar results.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Case-Control Study, nested case-control study, Dose-response relationship, Healthy Worker Effect, Odds Ratio, confidence interval, Cumulative Exposure.

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