Risk of lung cancer mortality after exposure to radon decay products in the Beaverlodge cohort based on revised exposure estimates.

Exposures to radon decay products have been re-estimated for 65 men who died of lung cancer between 1950 and 1980, and 126 matched controls selected from the Beaverlodge cohort of 8,487 workers at the Beaverlodge mine in Northern Saskatchewan. The revised exposure estimates were based on a more thorough review of individual employment records for the study subjects than originally conducted, together with historic data from area-specific measurements of exposure rates in the mine. The revised cumulative exposures are approximately 60% higher than the original exposure estimates, which were based on mine-wide averages for those exposures incurred prior to 1967, and which used geometric rather than arithmetic means for area exposure rates. Despite the increase in estimated exposures using the revised estimates, the excess relative risk per 100 working level months has increased from 2.70 to 3.25, most likely due to a substantial reduction in random exposure measurement error. The new data show similar modifying effects of risk by time since exposure and age at risk as other studies of underground miners, but provide no evidence of an inverse exposure-rate effect, in contrast to a strong effect seen in the analyses based on the original exposure estimates.