Abstract
The article summarizes the most recent results from the cohorts of uranium miners, particularly the risks at low exposures and the risk models with modifying effects of exposure rate, age ...and time since exposure, which are used for the calculation of lifetime risks (LRs). The excess relative risks per unit exposure (ERR/WLM) arising from low exposures were found up to 10 times higher than the crude risk coefficients. For studies that reported models with modifying effect of age, time since exposure and exposure rate, LRs were calculated using the BEIR VI projection. These LRs were also calculated for a model with effect modification on the annual exposure rate. The results were prepared for the UNSCEAR report on ‘Lung cancer from exposure to radon.’(1)
A combined analysis of three case-control studies nested in three European uranium miner cohorts was performed to study the joint effects of radon exposure and smoking on lung cancer death risk. ...Occupational history and exposure data were available from the cohorts. Smoking information was reconstructed using self-administered questionnaires and occupational medical archives. Linear excess relative risk models adjusted for smoking were used to estimate the lung cancer risk associated with radon exposure. The study includes 1046 lung cancer cases and 2492 controls with detailed radon exposure data and smoking status. The ERR/WLM adjusted for smoking is equal to 0.008 (95% CI: 0.004–0.014). Time since exposure is shown to be a major modifier of the relationship between radon exposure and lung cancer risk. Fitting geometric mixture models yielded arguments in favor of a sub-multiplicative interaction between radon and smoking. This combined study is the largest case-control study to investigate the joint effects of radon and smoking on lung cancer risk among miners. The results confirm that the lung carcinogenic effect of radon persists even when smoking is adjusted for, with arguments in favor of a sub-multiplicative interaction between radon and smoking.
In cohort studies, the regression estimates of excess relative risk use information on background rates corresponding to zero exposures. These are usually estimated internally from cohorts. This ...needs some stratification by factors like age, calendar period or birth cohort. In addition, such background rates depend on the regression model. The aim of the presentation is to assess which factors are substantial for the stratification. Results are given form Czech, French, and German cohorts of uranium miners. In the model that takes into account cumulated radon exposure and calendar period specific excess relative risks including modifying effects of age at exposure and time since exposure, the effect of calendar year stratification period was found non-significant (p = 0.23). This is in line with approaches used in evaluation of 11 studies of underground miners by the National Cancer Institute in 1994 that used only age stratification. In addition, the estimates of excess relative risk per unit exposure for strata excluding calendar year were higher in the present joint study by 23% from estimates when age, calendar year, and cohort are used in stratification. The likely reason is that calendar period stratification remove the calendar period variability in exposure.
The aim of the present study was to evaluate the risk of lung cancer from combined exposure to radon and smoking. Methodologically, it is based on case-control studies nested within two Czech cohort ...studies of nearly 11,000 miners followed-up for mortality in 1952-2010 and nearly 12,000 inhabitants exposed to high levels of radon in homes, with mortality follow-up in 1960-2010. In addition to recorded radon exposure, these studies use information on smoking collected from the subjects or their relatives. A total of 1,029 and 370 cases with smoking information have been observed in the occupational and environmental (residential) studies, respectively. Three or four control subjects have been individually matched to cases according to sex, year of birth, and age. The combined effect from radon and smoking is analyzed in terms of geometric mixture models of which the additive and multiplicative models are special cases. The resulting models are relatively close to the additive interaction (mixing parameter 0.2 and 0.3 in the occupational and residential studies, respectively). The impact of the resulting model in the residential radon study is illustrated by estimates of lifetime risk in hypothetical populations of smokers and non-smokers. In comparison to the multiplicative risk model, the lifetime risk from the best geometric mixture model is considerably higher, particularly in the non-smoking population.
The present study is based on 9978 Czech uranium miners with 1141 lung cancer deaths observed in an updated follow-up 1952-2010 and corresponding to 31 years of mean follow-up. The objectives of the ...study are to obtain more reliable estimates for the exposure-response relationship, including factors that modify this relationship. Lung cancer in relation to cumulative exposure to radon decay products is linear with substantial modifications by time since exposure, age at exposure and exposure rate using exposure windows. The crude excess relative risk (ERR) per unit exposure in working level months (WLM) in the cohort is 0.0097 (90% confidence interval (CI) 0.0074-0.0127). The ERR WLM corresponding to exposure rates below 7 working levels (WL) is substantially higher − 0.0145 (90% CI 0.0109-0.0193). In the final model, the inverse effect of exposure rate is observed for high exposure rates >7 WL with the ERR WLM reduced to 31%. The ERR WLM decreases to 32% and 9% in periods 20-29 and 30 +years since exposure in comparison to the period of 5-19 years since exposure. Simultaneously, the ERR WLM decreases with age at exposure − 63% and 49% at ages 30-39 and 40 +years in comparison to age at exposure <30 years.
It is well established that high radon exposures increase the risk of lung cancer mortality. The effects of low occupational exposures and the factors that confound and modify this risk are not clear ...and are needed to inform current radiation protection of miners. The risk of lung cancer mortality at low radon exposures (< 100 working-level months) was assessed in the joint cohort analysis of Czech, French, and Canadian uranium miners, employed in 1953 or later. Statistical analysis was based on linear Poisson regression modeling with grouped cohort survival data. Two sensitivity analyses were used to assess potential confounding from tobacco smoking. A statistically significant linear relationship between radon exposure and lung cancer mortality was found. The excess relative risk per working-level month was 0.022 (95% confidence intervals: 0.013–0.034), based on 408 lung cancer deaths and 394,236 person-years of risk. Time since exposure was a statistically significant modifier; risk decreased with increasing time since exposure. A tendency for a decrease in risk with increasing attained age was observed, but this was not statistically significant. Exposure rate was not found to be a modifier of the excess relative risk. The potential confounding effect of tobacco smoking was estimated to be small and did not substantially change the radon–lung cancer mortality risk estimates. This joint cohort analysis provides strong evidence for an increased risk of lung cancer mortality from low occupational radon exposures. The results suggest that radiation protection measures continue to be important among current uranium miners.
ObjectivesEpidemiological studies of underground miners have provided clear evidence that inhalation of radon decay products causes lung cancer. Moreover, these studies have served as a quantitative ...basis for estimation of radon-associated excess lung cancer risk. However, questions remain regarding the effects of exposure to the low levels of radon decay products typically encountered in contemporary occupational and environmental settings on the risk of lung cancer and other diseases, and on the modifiers of these associations. These issues are of central importance for estimation of risks associated with residential and occupational radon exposures.MethodsThe Pooled Uranium Miner Analysis (PUMA) assembles information on cohorts of uranium miners in North America and Europe. Data available include individual annual estimates of exposure to radon decay products, demographic and employment history information on each worker and information on vital status, date of death and cause of death. Some, but not all, cohorts also have individual information on cigarette smoking, external gamma radiation exposure and non-radiological occupational exposures.ResultsThe PUMA study represents the largest study of uranium miners conducted to date, encompassing 124 507 miners, 4.51 million person-years at risk and 54 462 deaths, including 7825 deaths due to lung cancer. Planned research topics include analyses of associations between radon exposure and mortality due to lung cancer, cancers other than lung, non-malignant disease, modifiers of these associations and characterisation of overall relative mortality excesses and lifetime risks.ConclusionPUMA provides opportunities to evaluate new research questions and to conduct analyses to assess potential health risks associated with uranium mining that have greater statistical power than can be achieved with any single cohort.
Abstract
The International Commission on Radiological Protection (ICRP) publishes guidance on protection against radon exposure in homes and workplaces. ICRP Publication 137 recommends a dose ...coefficient of 3 mSv per mJ h m−3 (~10 mSv WLM−1) to be used in most circumstances of radon exposure, for workers in buildings and in underground mines. Recently, United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reviewed radon epidemiology and dosimetry and concluded that its established dose coefficient of 1.6 mSv per mJ h m−3 (5.7 mSv WLM−1) should be retained for use in its comparisons of radiation exposures from different sources in a population. This paper explains and compares the reviews of the scientific evidence from UNSCEAR and ICRP. It is shown that the UNSCEAR and ICRP reviews are consistent and support the use of the ICRP reference dose coefficients for radiation protection purposes. It is concluded that the ICRP dose coefficient should be used to calculate doses to workers.
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