Study on the relationship between exposure dose and CT dose index for various CT scanners using Monte Carlo simulation and human voxel phantoms

Purpose: WAZA-ARI is the web-based open system for X-ray CT dose calculator, which has been developed by NIRS and Oita University of Nursing and Health Sciences and the Japan Atomic Energy Agency(JAEA) [1]. We constructed source models based on actual measurements. The selectable CT scanners in WAZA-ARI are still not enough despite the continuing addition of CT scanners because the CT developers deliver a steady stream of new products. In this study, we investigate the relationship between exposure dose and CT dose index(CTDI) for various CT scanners in WAZA-ARI system and categorized CT sources based on parameter of radiation quality and fluence distribution in order to calculate organ dose for arbitrary CT models.Methods: The organ doses in CT exposure were calculated using Monte Carlo code, PHITS and Japanese adult voxel phantoms developed by JAEA [2]. We calculated the organ doses and CTDIs for about fifty CT sources. We investigated the relationship between the organ dose and CTDI in typical CT exposure for head and body.Results: The calculated organ doses per CTDI free air depended on the effective energy and the fluence distribution of X-ray from CT scanner. The radiation quality depended on the ratio of CTDI center and CTDI free air, and the fluence distribution depended on the ratio of CTDI peripheral and CTDI free air. The ratio of CTDI center/peripheral and CTDI free air was useful to categorized CT sources, and CT scanners with near CTDI ratios showed near exposure doses per CTDI free air.Conclusions: CT sources were categorized using The ratio of CTDI center/peripheral and CTDI free air. Existing calculated organ doses data for CT scanners were diverted to the dose calculation for CT scanner with near CTDI ratios.International Conference on Monte Carlo Techniques for Medical Applications (MCMA2017