Non-linear relationship of cell hit and transformation probabilities in a low dose of inhaledradon progenies

Abstract

Cellular hit probabilities of alpha particles emitted by inhaled radon progenies in sensitivebronchial epithelial cell nuclei were simulated at low exposure levels to obtain useful datafor the rejection or support of the linear-non-threshold (LNT) hypothesis. In this study,local distributions of deposited inhaled radon progenies in airway bifurcation models werecomputed at exposure conditions characteristic of homes and uranium mines. Then,maximum local deposition enhancement factors at bronchial airway bifurcations, expressedas the ratio of local to average deposition densities, were determined to characterise theinhomogeneity of deposition and to elucidate their effect on resulting hit probabilities. Theresults obtained suggest that in the vicinity of the carinal regions of the central airways theprobability of multiple hits can be quite high, even at low average doses. Assuming auniform distribution of activity there are practically no multiple hits and the hitprobability as a function of dose exhibits a linear shape in the low dose range.The results are quite the opposite in the case of hot spots revealed by realisticdeposition calculations, where practically all cells receive multiple hits and thehit probability as a function of dose is non-linear in the average dose range of10–100 mGy.