  Cellular hit probabilities of alpha particles emitted by inhaled radon
progenies in sensitive bronchial epithelial cell nuclei were simulated at low
exposure levels to obtain useful data for the rejection or in support of the
linear-non-threshold (LNT) hypothesis. In this study, local distributions of
deposited inhaled radon progenies in airway bifurcation models were computed at
exposure conditions, which are characteristic of homes and uranium mines. Then,
maximum local deposition enhancement factors at bronchial airway bifurcations,
expressed as the ratio of local to average deposition densities, were
determined to characterize the inhomogeneity of deposition and to elucidate
their effect on resulting hit probabilities. The results obtained suggest that
in the vicinity of the carinal regions of the central airways the probability
of multiple hits can be quite high even at low average doses. Assuming a
uniform distribution of activity there are practically no multiple hits and the
hit probability 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
realistic deposition calculations, where practically all cells receive multiple
hits and the hit probability as a function of dose is non-linear in the average
dose range of 10-100 mGy.
