Experimental studies on the post carbon-ion therapy

The purpose of this study is to find and suggests an optimum therapeutic ion beam for the next generation of Heavy Ion Medical Accelerator in Chiba (HIMAC) clinical trial. For this aim, we compare the biological effectiveness of light ions and heavy ions for tumors of which therapeutic gain of carbon ions is relatively low. One of the tumors responding well to carbon ions is malignant melanomas (MM) while squamous cell carcinomas (SCC) show response comparable to photon radiotherapy. It is possible that the two types of tumors are different in radiosensitivity to carbon ions, provided that the clinical difference between the two tumors is due to any biological reasons. We will use more than 10 MM and 10 SCC of human origin, and compare radiosensitivities of each cell line in vitro and in vivo. The ions we use here are both lighter and heavier than carbon ions. We have obtained survival curve parameters for 9 different MM cells and 8 SCC cells. The α/β ratio for MM and SCC cells to X-rays or carbon beam showed different spectrum. It was found that each one strain could be used for radiobiological experiment after the tumor inplantation. Biological uniformity of spread-out Bragg peak (SOBP) that has been calculated and designed to produce a He-150 MeV/u-6 cm-SOBP beam showed good enough uniformity for biological experiments. (author)