Comparisons of Calculated Respiratory Tract Deposition of Particles Based on the Proposed NCRP Model and the New ICRP66 Model

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Abstract
Task Groups of the National Council on Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP) have independently revised respiratory tract dosimetry models of inhaled radioactive aerosols. Both models contain modules for calculating inhaled particle deposition. In this report, the deposition of particles in the respiratory tract was calculated based on both the NCRP and the ICRP66 models, under the same particle size distribution, lung volume, and breathing conditions. The results indicate that the largest discrepancy between the two models is for ultrafine particles, where the ICRP66 model predicts a lower tracheobronchial deposition and a higher pulmonary deposition than the NCRP model. This difference is attributed to the fact that the ICRP66 model does not take into account the enhanced diffusional deposition due to the effect of the entrance configuration of a bifurcation. This may have significant implications on dose estimates of inhaled ultrafine particles, including radon and radon progeny.