Abstract
Up to March 2009, over 4500 patients have been treated in HIMAC, and some kinds of tumor, for example the malignant melanoma showed a decrease of survival rate in contrast to high local control rate. It is an important subject to control tumor distant metastasis for future radiotherapy. The effects of radiation to metastasis must be clarified fundamentally. The aim of this study is to clarify the radiosensitivity of mouse melanoma cell line having high-metastatic potential to heavy-ion and photon beams, and to examine the inhibitory effects of radiations to metastasis. B16/BL6 cell line was used as high metastatic cell line. Carbon-ion beams (C-ions) accelerated with 290 MeV/u as high LET and X-rays or γ-rays as low LET beams. <in vitro> Survival curve of B16/BL6 to X-rays showed large shoulder, and RBE value of C-ions was 1.6. Horizontal migration was enhanced by radiations using wound-healing assay. In contrast, matrigel invasion assay showed that vertical migration was suppressed by C-ions. <in vivo> Survival of cells in a tumor was obtained using in vivo-in vitro assay, and the survival curve of even C-ions showed big shoulder. The RBE was 1.9 bigger than in vitro assay. In addition, RBE obtained from tumor growth delay analysis was too large, 3.7. The effect of radiations to metastasis was examined using spontaneous lung metastasis model. The lung metastatic nodules were decreased by C-ions compared with X-rays. Furthermore, survival of mice was extended by C-ions compared with non-irradiation and X-rays irradiation groups. It was suggested that high LET beams like C-ions have a potential to inhibit metastasis significantly more than low LET beams as X-rays and γ-rays.
