The Influence of Adopting New Reference Breathing Parameters on ICRP66 Model on the Regional Deposition of the Inhaled Attached Radon-222 Daughters Within the Human Airways

The radiation dose from internal radiation exposure is difficult to measure directly and hence different lung models were developed. The dose on the lung is the result of the regional deposition of aerosols carrying radon daughters in the respiratory tract. Deposition of aerosols can be take place during inhalation and exhalation in the 5 regions of the respiratory tract due to variation of aerosol sizes and other biological factors such as breathing rate. In this paper, a modified breathing rate is instead applied on the assumptions developed by the ICRP66 model to analyze the regional deposition of radioactive aerosols and a comparison has been made with the result of ICRP66 model deposition. According to the result, as the diameter of aerosols increases from 1 to 10 μm, the percentage deposition fraction in extrathoracic regions, in ET1 region increases from 6.53% to 48.43% and in ET2 region increases from 7.3% to 50.33%. The aerodynamic deposition of the attached fraction of radon aerosols along the bronchial regions (bronchi (BB), and bronchiolar (bb) region) is found small and almost constant. For 1 μm diameter aerosols, the percentage deposition is found 0.82%, for 5 μm diameter aerosols, the deposition is predicted 2.56% and at 10 μm the deposition is predicted about 1.93% in bronchi (BB) region. In the bronchiolar region (bb) for 1 μm aerosols, the deposition predicted is 1.5% and at 10 μm about 0.88% is predicted. The deposition of small size attached fraction of radon aerosols is found maximum in the alveolar region as compared to other regions of the respiratory tract and the deposition becomes almost negligible for large size aerosols in this region.