A 10-year follow-up study of yearly indoor radon measurements in homes, review of other studies and implications on lung cancer risk estimates.

Uncertainty on long-term average radon concentration has a large impact on lung cancer risk assessment in epidemiological studies. The uncertainty can be estimated by year-to-year radon concentration variability, however few data are available. In Italy a study has been planned and conducted to evaluate year-to-year radon variability over several years in normally inhabited dwellings, mainly located in Rome. This is the longest study of this kind in Europe; repeat radon measurements are carried out for 10 years using LR-115 radon detectors in the same home in consecutive years. The study includes 84 dwellings with long-term average radon concentration ranging from 28 to 636 Bq/m3. The result shows that year-to-year variability of repeated measurements made in the same home in different years is low, with an overall coefficient of variation of 17%. This is smaller than most of those observed in studies from other European countries and USA, ranging from 15% to 62%. Influencing factors that may explain the differences between this study and other studies have been discussed. Due to the low yearly variability estimated in the present 10-year study, a negligible impact on lung cancer risk estimate for the Italian epidemiological study is expected.