The Significance of Enhanced Radionuclide Deposition at Bronchial Bifurcations

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Abstract
Experiments have been conducted to quantitate the deposition patterns of monodisperse aerosols in surrogates of the human upper respiratory tract. Laryngeal casts and most upper airway bifurcations were sites of preferential particle deposition. Highly concentrated deposits were detected at carinal ridges within bifurcation zones. Together with impaired mucociliary clearance at branching sites, this initial deposition pattern results in localized accumulations of radionuclides within bifurcation zones. For inhaled radon progeny radiation doses are calculated for 3 regions of bronchial airways: tubular airway segments, bifurcation zones (including the carina), and carinal ridges. These calculations indicate that enhanced deposition at branching sites leads to significantly higher doses to epithelial cells located at bifurcations than along tubular airway segments. If, however, cell killing is included in the analysis of lung cancer risk, it reduces the carcinogenic potential at bifurcation sites, particularly at high doses.

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