The Microdosimetry of Radon Decay Products in the Respiratory Tract

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Abstract
The purpose of this study was to develop methods for calculating the probability density in specific energy for cell nuclei of the respiratory tract epithelium irradiated by inhaled radon and daughter products. Microdosimetry also provides the probability that cell nuclei may be hit by alpha particles, the probability that cell nuclei are completely missed, and the mean (absorbed) dose to cell nuclei. Such information is useful for interpreting the significance of an inhalation exposure to radon and daughters. The secretory and basel cell nuclei were considered separately as potential targets of biological importance for exposure to radon daughters. A 30 day (0.023 WLM) and a 30 year (8.45 WLM) exposure to a reference atmosphere representing an average exposure to the US population to a radon concentration of 37 Bq.m-3 (1 pCi.l-1) in disequilibrium with its daughters were considered for sample calculations. About 0.3% and 10% of cell nuclear sites would be hit once for 30 day and 30 year exposures, respectively. Most cell nuclear sites (80-90%) would be missed by the 30 year exposure to alpha particles. The main, lobar, and segmental bronchi (generations 1-4) have the highest fraction of cell nuclei irradiated; these are also the epithelial tissues from which most bronchial tumours originate in humans exposed to radon atmospheres. The average 30 year reference atmosphere doses to secretory and basal cell nuclei in the segmental bronchi were 0.3 Gy and 0.2 Gy (30 rad and 20 rad), respectively. These values correspond to 0.035 Gy.WLM-1 and 0.024 Gy.WLM-1, respectively. For the whole bronchial tree, the average absorbed dose per unit exposure was 0.014-0.015 Gy.WLM-1 (1.4-1.5 rad.WLM-1).

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