Non-linear relationship of cell hit and transformation probabilities in low dose of inhaled radon progenies

TL;DR

This study uses simulations to explore how radon progeny deposition affects cell hit probabilities at low doses, revealing non-linear effects due to hot spots that challenge the linear-non-threshold hypothesis.

Contribution

It introduces a detailed simulation approach to analyze inhomogeneous radon progeny deposition and its impact on cell hit probabilities at low exposure levels.

Findings

Multiple hits are likely near airway bifurcations at low doses.

Uniform activity distribution results in linear hit probability at low doses.

Realistic hot spots cause non-linear hit probability, with most cells receiving multiple hits.

Abstract

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.