Implications of a two-stage clonal expansion model to indoor radon risk assessment

Spreadsheet macro programs for calculations of exact hazard and probability of having contracted cancer were used to study the implications of the lung cancer model of Moolgavkar et al. Excess lifetime risk ELR and loss of life expectancy LLE were calculated from the annual values of hazard and probability, using published life tables. The influence of various factors on ELR and LLE was studied, as well as the lifetime risk projection in epidemiological studies. At indoor concentrations, ELR and LLE are coarsely proportional to lifetime exposure. The main factors determining the proportionality coefficient are 1. Smoking status, 2. General life expectancy, 3. Exposure schedule, and 4. Sex. For constant domestic exposure, the sex is less important, because the longer life of women is compensated by the lower hazard. ELR and LLE for a population with 30% smokers and life expectancies of 72.1 y and 79.5 y for men and women, respectively, are 56 per million per WLM and 860 y per million per WLM, respectively. For an exposure schedule with one high radon period, the mean age during the period becomes important, and the age-specific values for men and women differ from each other. Furthermore, the model predicts that case-control epidemiological studies overestimate the lifetime risk by an amount which may arise to several tens of percent.