26. Significance of Fractionated Irradiation for the Biological Therapeutic Gain of Carbon Ions
Koichi Ando, Sachiko Koike, Akiko Uzawa, Nobuhiko Takai, Takeshi Fukawa, Yoshiya Furusawa, Mizuho Aoki, Chisa Oohira, Manami Monobe, Ryonfa Lee, Masao Suzuki and Kumie Nojima
Keywords: relative biological effectiveness, mouse, tumor, skin
It is well established that the RBE (relative biological effectiveness) for cell killing depends on LET (linear energy transfer), and that a maximum RBE is observed at ~150 keV/µm. However, the therapeutic gain depends on the ratio of the RBEs for the effects on the cancer cell population and the effects on normal tissues. The RBE of a given radiation quality depends on LET but also on dose, biological system and effect, and irradiation conditions. There are no data available to answer the question: which LET is suitable to improve the biological therapeutic gain of carbon ions? Here, we selected 3 different LET values of 290 MeV/u carbon ions, and compared the relative biological effectiveness between tumor growth retardation and skin damage using a murine transplantable tumor. Larger RBE values for tumors than the skin type were obtained when carbon ions of intermediate LET were delivered daily for 2 through 5 fractions (Fig. 20). The biological therapeutic gain would be high for the carbon ion SOBP when the number of fractions has been correctly selected in clinical trials.
Publications:
1) Koike, S., Ando, K., Uzawa, A., Takai, N., Fukawa, T., Furusawa, Y., Oohira, C., Aoki, M., Lee, R., Suzuki M. and Nojima, K. Radiation Protection Dosimetry +99, 405-408, 2002.
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