Radon exposure assessment and dosimetry applied to epidemiology and risk estimation.

Epidemiological studies of underground miners provide the primary basis for radon risk estimates for indoor exposures as well as mine exposures. A major source of uncertainty in these risk estimates is the uncertainty in radon progeny exposure estimates for the miners. Often the exposure information is very incomplete, and exposure estimation must rely on interpolations, extrapolations and reconstruction of mining conditions decades before, which might differ markedly from those in more recent times. Many of the measurements that were carried out-commonly for health protection purposes-are not likely to be representative of actual exposures. Early monitoring was often of radon gas rather than of the progeny, so that quantifying exposure requires an estimate of the equilibrium fraction under the conditions existing at the time of the reported measurement. In addition to the uncertainty in radon progeny exposure, doses from gamma radiation, inhaled radioactive dust, and thoron progeny have historically been neglected. These may induce a systematic bias in risk estimates and add to the overall uncertainty in risk estimates derived from the miner studies. Unlike other radiogenic cancer risk estimates, numerical risk estimates derived for radon from epidemiology are usually expressed as a risk per unit exposure rather than as a risk per unit dose to a target tissue. Nevertheless, dosimetric considerations are important when trying to compare risks under different exposure conditions, e.g. in mines and homes. A recent comparative assessment of exposure conditions indicates that, for equal radon progeny exposures, the dose in homes is about the same as in mines. Thus, neglecting other possible differences, such as the presence in mines of other potential airborne carcinogens, the risk per unit progeny exposure should be about the same for indoor exposures as observed in miners. Results of case-control studies of lung cancer incidence in homes monitored for radon are reasonably consistent with what would be projected from miner studies. Measurements of exposure in these indoor case-control studies rely on different types of detectors than those used in mines, and the estimates of exposure are again a major source of uncertainty in these studies.