Modeling Energy Deposition and Cellular Radiation Effects in Human Bronchial Epithelium by Radon Progeny Alpha Particles

Abstract

Energy deposition and cellular radiation effects arising from the interaction of single 218Po and 214Po alpha particles with basal and secretory cell nuclei were simulated for different target cell depths in the bronchial epithelium of human airway generations 2, 4, 6, and 10. To relate the random chord lengths of alpha particle tracks through spherical cell nuclei to the resulting biological endpoints, probabilities per unit track length for different cellular radiation effects as functions of LET were derived from in vitro experiments. The radiobiological data employed in the present study were inactivation and mutation (mutant frequency at the HPRT gene) in V79 Chinese hamster cells and inactivation and transformation in C3H 10T1/2 cells. Based on computed LET spectra and relative frequencies of target cells, probabilities for transformation, mutation, and cell killing in basal and secretory cells were computed for a lifetime exposure of 20 WLM. While predicted transformation probabilities were about two orders of magnitude higher than mutation probabilities, they were still about two orders of magnitude lower than inactivation probabilities. Furthermore transformation probabilities for basal cells are generally higher than those for secretory cells, and 214Po alpha particles are primarily responsible for transformations in bronchial target cells.

Multiple Stressor Effects of Radon and Phthalates in Children: Background Information and Future Research

“…In many micro-dosimetric studies on the absorbed dose in the HRT due to inhaled radon progeny, the survival or death of the target cells irradiated by α-particles was not taken into account. In reality, some of these target cells would not survive [140][141][142], which should be excluded in the computations of the average absorbed dose. Interestingly, consideration of probabilities for cell-killing by applying the effect-specific track length model [140][141][142], which expressed the probability per unit track length in the cell nucleus (chord length) for cell-killing as a function of the LET of the α-particles, would significantly change this average absorbed dose [143].…”

Microdosimetric calculation of absorption fraction and the resulting dose conversion factor for radon progeny

“…The centers of the nuclei were chosen randomly and the total volume of all nuclei was calculated. The nuclei were chosen to be spherical, with a diameter of 9 µm in BB and 8 µm in bb, after Hofmann et al [13]. The nuclei were added one by one until the volume abundance given by Mercer et al [11] was achieved.…”

“…They were recently employed by Hofmann et al [13] who made a linear fit to them with steps of 5 µm. The original data by Mercer et al [11] were given for the large bronchi (diameters 3-5 mm), small bronchi (diameters 1-3 mm) and bronchiole (diameter <1 mm).…”

Absorbed fraction and dose conversion coefficients of alpha particles for radon dosimetry

“…Different authors used various assumptions about the thickness of the mucous layer. For example, Hofmann et al (2000) used 8 µm as the mucus thickness, which is independent of the generation number of the airway tube, while Hui et al (1990) assumed a constant mucous blanket thickness of 15 µm.…”