222Rn Daughter Dosimetry in the Syrian Golden Hamster Lung

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A detailed morphometric description of the dimensions of airways, the branching patterns, and the epithelial cell frequencies in the respiratory tract of the Syrian golden hamster has been completed. We used these data to construct a mathematical model of the deposition of inhaled particles and their subsequent regional translocation during extracellular lung clearance. The number of disintegrations per year was calculated for 218Po and 214Po in each airway group using reference radioactive atmospheres. Disintegrations were converted to absorbed dose using the depth-dose distribution in a cylindrical tissue annulus for each alpha particle energy. The resulting doses show a significant difference between the types of cells and locations receiving maximum exposure when the model of the hamster lung was compared to current models of the human respiratory tract. The dose to basal cells in the subsegmental bronchi is 0.4–1.6 rad per working level year (WLY). The mean dose to basal cells is 2–3 rad per WLY. Peripheral basal cells may receive doses approximately equal to doses received by basal cells in the central airways. Moreover, Clara cells in the terminal bronchioles may also receive 2–3 rad per WLY. Since Clara cells have been implicated in hamster lung carcinogenesis, the dose to these differentiated cells may be relevant to inducing tumors. In contrast, models of the human lung suggest that the highest dose to all types of cells is in the higher airways (subsegmental bronchi) and that the cancer-related dose is 3–20 rad per WLY for identical 222Rn-laden atmospheres. Although these results are subject to the limitations inherent in the mathematical modeling of biological phenomena, they indicate that the frequency, location, and morphology of 222Rn-induced lung cancer in hamsters may not be a straightforward indication of human response when exposures are expressed in WLY.

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