Dose calculations for the respiratory tract from inhaled natural radioactive nuclides as a function of age--II. Basal cell dose distributions and associated lung cancer risk.

Abstract

Dose calculations for inhaled radon decay products presented in Part I (Ho79) have revealed that the doses to tracheobronchial and pulmonary compartments of the ICRP lung model are significantly dependent on age. From a consideration of the nonuniform dose distribution within the tracheobronchial region, doses are now calculated for the bronchial epithelium basal cells which are commonly regarded as the critical target for the induction of lung cancer. For the simulation of deposition and clearance mechanisms a refined mathematical model for postnatal growth of the human respiratory tract was developed on the basis of the Weibel model A. A reference atmosphere of 1 pCi/l for each nuclide with a mean respiratory minute volume, corresponding to a mean physical activity, was used to determine doses for the basal cells in different generations of the tracheobronchial tree as functions of age. The results obtained show again a strong dependence on age. In general a continuous decrease of dose with increasing age can be seen, with distinct differences between the various generations. If, however, the physical activity distribution and the ratio for the decay products as already defined in Part I are used, maximum dose values appear again in all generations at the age of about six years. Application of data on the relative risk of the induction of various malignancies versus age, taken from the BEIR report, results in even more pronounced dose maxima with a significantly higher radiation risk for children between birth and ten years of life of about one order of magnitude as compared to adults.