@misc{oai:repo.qst.go.jp:00063196,
 author = {Okayasu, Ryuichi and Kato, Takamitsu and Fujimori, Akira and Noguchi, Miho and Fujii, Yoshihiro and 岡安 隆一 and 加藤 宝光 and 藤森 亮 and 野口 実穂 and 藤井 義大},
 month = {Aug},
 note = {At the National Institute of Radiological Sciences (NIRS), over 4000 cancer patients have been treated by heavy ions with an impressive success rate. There are clinical, physical and biological factors behind this achievement, and in this presentation a few critical biological issues are discussed. Besides the physical advantage of the dose distribution of heavy ions, two important biological factors exist; one of them the inhibition of DNA double-strand break (DSB) repair by heavy ions and the other the reduced variation of cell survival levels throughout the cell cycle. The repair of DNA DSB was examined using constant field gel electrophoresis as well as gamma-H2AX assay, and both techniques clearly showed a significant inhibition of initial rejoining of DSBs induced by 70 keV/µm carbon ions. The degree of repair inhibition seems to be reflected in the radiation cell survival level. Using synchronized CHO cells, we investigated cell survival levels throughout the cell cycle with carbon ions, and the result was compared with that with X-rays. Our data indicated that much less variation in the cell survival level was observed when carbon ions were used to irradiate cells. Moreover, gene expression studies using a unique method developed at NIRS provided new insight into biological damage induced by heavy ions. These data together provide biological reasons for the successful outcome reported at the heavy ion facility at NIRS., Joint Symposium on Carbon Ion Therapy},
 title = {Repair of DNA double strand breaks induced by heavy ion irradiation},
 year = {2009}
}