Compartment model for radon-induced absorbed dose in lungs

Abstract

Inhalation of radon gas and radon daughters has since a long time been reported as the second leading cause of lung cancer after smoking. The biological hazards make it therefore important to quantify the absorbed doses from radon and radon daughters. The first aim of the study was to reconstruct the Human Respiratory Tract Model, presented by ICRP, to describe the biokinetics, i.e. movement of radon and radon daughters after inhalation for members of the public. The biokinetic model was implemented in the software tool Ecolego and was supplemented with Human Alimentary Tract Model and systemic models of radon, polonium, lead, and bismuth for a complete description of internal exposure. The final biokinetic model enables the user to acquire time-integrated activity (Ã) for combinations of 1) radon and radon daughters, 2) different modes of particle size distribution of radon daughters in air, 3) for members of the public of ages 3 months old, 1 year old, 5 years old, 10 years old, 15 years old and adults defined by ICRP and 4) genders for 15 years old and adults. The model was in a first step bench-marked against the internal dose calculation software Taurus, through comparison of à in the lungs, which resulted in approximately 20% relative bias between the implemented biokinetic model and Taurus. For an overall evaluation of the biokinetic model, the effective dose for radon daughters was calculated to be 18.22 mSv per WLM, which is in the range of values (7–21.1 mSv per WLM) obtained by other researchers. A secondary aim was to study how absorbed doses from emitted α-and β particles following the decay of radon and radon daughters are distributed between tissues of the lungs. Absorbed doses were generated using the software program IDAC-Dose 2.1. In addition, values of S coefficients for combinations of source regions and target tissues inside the respiratory tract were incorporated in the software giving approximative values on absorbed doses and associated uncertainties. The absorbed dose from inhaled radon gas were found to be two orders of magnitude smaller than absorbed doses from inhaled radon daughters. The highest absorbed doses were, as expected, found to be from emitted α particles from 218Po- and 214Po-decay in nearly all tissues of the lungs.