Speaker
Description
In carbon-ion radiotherapy, the treatment plan is verified by comparing the planned dose and measured dose before treatment. The dose measurement is limited to a portion of the three-dimensional (3D) irradiation region of interest. Gel dosimeters can measure the 3D absorbed dose distribution using the reaction between radiation-sensitive dye and radicals generated by radiation exposure. However, gel dosimeters have the problem of low responsiveness in the position where the dose is localized, such as Bragg peak [1]. In order to solve the problem, this study was performed. Specifically, carbon-ion beams were irradiated onto micellar gel dosimeter and poly(vinyl alcohol) and iodide (PVA-I) gel dosimeter under various beam conditions, and then an optical absorbance and an optical density distribution was measured [2-3]. The results were compared with the absorbed dose distribution estimated by Particle and Heavy Ion Transport code System (“PHITS”) [3]. The radical concentration distribution generated in the gel dosimeters was also estimated by liner energy transfer (LET) calculated using “PHITS”. Based on these results, we considered the responsiveness of the gel dosimeters at Bragg peak and spread-out Bragg peak (SOBP). We will also introduce examples of the use of “PHITS” in a series of studies.
This collaborative study involved Yokohama National University, Toshiba Energy Systems and Solutions Corp. (Kawasaki, Japan), and Kanagawa Prefectural Hospital Organization. This study underwent an ethical review process and received approval from the Yokohama National University Institutional Review Board (YNU IRB 2020-7-9) on May 13, 2020, and from the Kanagawa Cancer Center (KCC IRB 2020-46), which is part of the Kanagawa Prefectural Hospital Organization, on June 29, 2020.
References
[1] K. Hayashi M. Toyohara, Y. Kusano, et al., “Behaviour and mechanism of micelle gel dosimeter for carbon-ion-beam irradiation”, Radiat. Phys. Chem. 179, (2021), 109191.
[2] K. Tadano, K. Hayashi, M. Toyohara, et al., “Elucidation of poly(vinyl alcohol) and iodide gel dosimeter characteristics by predicting changes in radical concentrations and measuring responsiveness to heavy ion beams”, Radiat. Phys. Chem. 197, (2022), 110167.
[3] T. Sato, Y. Iwamoto, S. Hashimoto, et al., “Features of Particle and Heavy Ion Transport code System (PHITS) version 3.02”, J. Nucl. Sci. Technol. 55(5-6), (2018), pp. 684-690.
