Biological studies toward the application to heavy-ion radiotherapy

Although understanding on biological mechanisms involved in heavy-ion radiotherapy such as relative biological effectiveness (RBE), oxygen enhancement ratio (OER), recovery and reoxygenation of hypoxic tumor cells has been progressed by recent Heavy Ion Medical Accelerator in Chiba (HIMAC) related research, there is still much to be learned about RBE for hypoxic tumor cells and α/β ratio for both tumors and critical normal tissues in fractionated heavy-ion therapy. Much progress has been also made on newly developing studies on presumably heavy-ion specific biological effects such as inhibition of tumor angiogenesis and metastases, bystander effect mediated by NO radicals. More studies toward their application to radiotherapy are certainly required. (author)