Ion beam radiation chemistry relevant to radiation therapy

放射線治療に関連するイオンビーム放射線化学

勝村 庸介; 山下 真一; Lin, M.; 前山 拓哉*; 室屋 裕佐*; Baldacchino, G.*; Jay-Gerin, J.-P.*; Meesungnoen, J.*; 村上 健*

Katsumura, Yosuke; Yamashita, Shinichi; Lin, M.; Maeyama, Takuya*; Muroya, Yusa*; Baldacchino, G.*; Jay-Gerin, J.-P.*; Meesungnoen, J.*; Murakami, Takeshi*

In Japan, cancer is the first place of the death rate and radiation treatment becomes more and more popular. Especially, ion beam treatment receives much attention because it is effective against even some radioresistant cancers. Consequently, several ion beam facilities have been constructed. Since about 70 % of our body is water, understanding of water radiolysis with ion beams is essential for the evaluation of the biological effect of ion beams. In the present experiment, radiolysis of water has been investigated with ions beams from He to Xe of a few hundreds MeV per u, which are provided at HIMAC facility installed in National Institute of Radiological Sciences. The -values of e, OH and HO as a function of LET at 100 ns after the energy deposition have been determined. The radical yields decrease but the HO yield increases with the increase of LET due to the track reaction. The experimental data is compared with the Monte Carlo simulation and it was found that the simulation could reproduce the results, indicating the validity of the simulation. Similar experiment has been done at the Bragg peak. The data were analyzed considering the contribution of secondary ions produced through the fragmentation reactions of the primary projectiles. The HIBRAC code can reproduce the experimental results successfully. In the high energy ion beam treatments, the evaluation of the secondary ions is inevitably important.