The ICRP Human Respiratory Tract Model for Radiological Protection

A new ICRP dosimetric model of the respiratory tract provides for the inhalability of airborne materials and describes deposition in specific extrathoracic and thoracic regions. Clearance is competitive between particle transport processes and absorption into blood. Reference values for particle transport rates are provided. In the absence of observations on specific radionuclide compounds, default values for rates of absorption into blood are given for materials classified as being rapidly, moderately, or slowly absorbed. Instead of calculating an average dose to the total lungs, the new model provides for calculating doses to specific tissues of extrathoracic and thoracic airways. By apportioning the ICRP tissue weighting factors among these tissues to account for differences in radiation sensitivity, values of equivalent dose are obtained for use in the ICRP dosimetric system.