Morphological Characteristics of Respiratory Tract on Inhalation Dose Assessments for Japanese Populations

Abstract

The Human Respiratory Tract Model (HRTM) proposed by the ICRP is used to assess internal doses due to inhalation of radioactive aerosols ¹⁾ . The morphological information on the respiratory tract in the HRTM was based on a few cases of Caucasians. In this study, we evaluated the morphological characteristics of the respiratory tract for Japanese using computed tomography to examine whether the HRTM could be adapted to other racial groups. Patients without disease affecting the analysis were selected and the diameter, length, and subcarinal angle to trachea axis were measured using software (Thoracic VCAR software, GE Healthcare Japan). As a result, we analyzed 100 males and 109 females. The diameter of the bronchi was slightly different from that in the HRTM because it was created from a cast replica and this study was implemented based on images taken during inspiration. Although the HRTM defines a bronchial structure as the symmetrical shape, differences in bronchial length were observed between the left and right lungs even if the bronchial generation was the same. The similar morphological characteristics have been reported in Chinese and Koreans^{2, 3)}. In the ICRP publication 66, tracheal and bronchial dimensions are correlated with patientʼs height, but no correlation was found in the present study. From an anatomical point of view, it is difficult to conclude that the HRTM reproduces the actual respiratory airway. How the differences affect particle deposition in the respiratory tract should be examined. This work was partially supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant No. JP20H00556.