Effects of Human Model Configuration in Monte Carlo Calculations on Organ Doses from CT Examinations

Abstract

A new dosimetry system, WAZA-ARI, is being developed to estimate the radiation dose in Computed Tomography (CT) examinations in Japan. Dose estimation in WAZA-ARI utilizes organ dose data that are derived by Monte Carlo calculations using the Particle and Heavy Ion Transport code System (PHITS). A Japanese adult male phantom, JM phantom, has been adapted as a reference human model in the calculations, because the physique and inner organ masses agree well with the average values for Japanese adult males. However, since each patient has individual physical characteristics, the effect of a patient’s body configuration on organ doses was studied by utilizing PHITS with another Japanese male model and the International Commission on Radiological Protection (ICRP) reference phantom. In addition, this paper describes computation conditions for the three human models, which were constructed in the form of voxel phantoms with different resolutions. Differences were observable among the phantoms in the dependences of the organ doses per air kerma on the position of the x-ray source running over the patient’s body. The source model definition, however, more strongly affected the patient doses in the same phantom.