Sensitivity of doses and associated uncertainties in bioassay estimates to ICRP Publication 66 Respiratory Tract Dosimetric Model with respect to the parameters: Ventilation rates, time budget, total and regional deposition, oral versus nasal breathing and clearance rates of compartments

Abstract

An analysis of the reliability of the ICRP's dose coefficients for intake of radionuclides, applied on the Human Respiratory Tract Dosimetry Model proposed in ICRP Publication No. 66 was carried out, with respect to the following variables: ventilation rates, time budget, total deposition, regional deposition for the four respiratory tract compartments (alveolar-interstitium, bronchioles, bronchi and extrathoracic), oral versus nasal breathing patterns, and variation in clearance rates of compartments. The analysis was done by calculating reliability factors defined as the square root of the ratio of larger to smaller dose coefficient calculated at the extreme values for the model parameter being tested, in intervals of values of the effective dose. Calculations for each of the variables were carried out for an adult, using these 12 radionuclides: 3H, 60Co, 90Sr, 95Zr, 106Ru, 125Sb, 131I, 137Cs, 210Pb, 226Ra, 238U and 239Pu. For AMAD = 0.1 mm the analysis associated with the total deposition in the compartments indicated a Reliability Category II. For AMADs = 1.0 and 10 mm the analysis associated with the deposition in the extrathoracic compartments indicated a Reliability Category II. For AMAD = 10 mm the deposition in the compartments of the tracheobronchial region also showed a Reliability Category II. Most results for all other parameters for the studied AMADs were found to be in Category I. The corresponding impacts on the uncertainties in the predicted bioassay results for these twelve radionuclides were also determined. This analysis is especially helpful when doses are estimated through bioassay measurements employing the ICRP Publication 66respiratory tract model.