Experience from retrospective radon exposure estimations for individuals in a radon epidemiological study using solid-state nuclear track detectors

The relation between increased risk of lung cancer and exposure to indoor radon is assessed in epidemiological studies. Both the quality and reliability of smoking data and the radon exposure data are of primary importance. Contemporary measurement of radon concentration in the dwellings of individuals in a case-control study is traditionally used to assess past history of radon exposure. These assessments are somewhat unreliable since presently measured radon concentration might not be representative for a given location long ago. The measurement of long-lived decay products from 222Rn remaining indoors on hard surfaces, such as glass, makes it possible to assess the exposure to indoor radon. At the Swedish Radiation Protection Institute, a combination of two different solid-state nuclear track detectors has been developed to assess the 210Pb activity implanted in glass surfaces by measuring 210Po alpha activity. This detector Ža RETRO detector. is used in the Swedish radon epidemiological case-control study of non-smokers with the aim to provide an alternative estimate of individual radon exposure and to evaluate the usefulness of RETRO measurements. A total of 576 different objects were found and 568 were measured. For 225 individuals, we measured two personal objects that had been in the same person’s possession for more than 20 years. The standard deviation of the average radon concentration obtained from these two objects had a median value of 13 Bq m3 indicating a precision of exposure of approximately 20%. The correlation between 210Po surface activity measured earlier and the mean values of radon concentrations in a number of Swedish dwellings is used to estimate the historical, average radon concentration. This average correlation factor seems also to be valid for measurements in the non-smoker epidemiological study.