Abstract
It is known that high LET heavy-ion radiation have a high RBE compared to low LET radiation such as X-ray and proton for the cell death, mutation induction and chromosome damage. Recently, it has been shown that heavy-ion radiation is effective in the treatment of recurrent colon cancer. However, it is still unclear what is the difference in the gastroenterological tumor control and the mechanisms between heavy-ion and X-ray radiation therapy. In the present study, we examined effects of carbon-ion and X-ray on the treatment of transplantable human colon cancer in Balb/c-nu/nu mice. HCT116 (8x104) and SW480 (7x105) cells were inoculated into right hind legs of mice and were irradiated with 27, 30, 33 Gy carbon-ion (C290, 50keV/um, SOBP) or X-ray when the xenograft tumors grew to a certain size. We found that both X-ray and carbon-ion radiation effectively suppressed tumor growth with dose-related manner. However, the tumors were re-grew in the X-ray irradiated mice after 2 weeks, in contrast, all the tumors were repressed and consequently the tumor size was remarkably decreased or completely disappeared without any relapse or re-growth. Tumor-supplying vessels were also reduced in carbon-ion irradiated mice compared to those of X-ray irradiated mice when examined one month later. Taken together, heavy-ion irradiation can radically control tumor growth compared to X-ray. Further studies on the influences of heavy-ion on cancer stem cells and the molecular pathological mechanisms need to be done.
