Host: The Japan Radiation Research Society
High liner energy transfer (LET) particle therapy has various advantages in terms of radiobiological effects as well as dose distribution, and had been expected to offer a therapeutic gain over conventional photon therapy. The biologic advantages of high LET radiation including neutrons and heavy charged particles, compared with low LET radiation like photons, are summarized as a decreased oxygen enhancement ratio, a diminished capacity for sublethal and potentially lethal damage repairs, and diminished cell cycle dependent radiosensitivity. However, no proof of these effects has been provided by clinical trials and related clinical researches. Hence, the radiation biological aspect of the high LET carbon beam therapy of various cancers were investigated by analyzing clinical results of carbon beam therapy of various cancers at NIRS. At least radiation resistant tumors as adenocarcinoma, adenoid cystic cancer, malignant melanoma and osteosarcoma were well locally controlled by carbon beams. The similar local control rates between the oxygenated and hypoxic cervical cancers indicated that high LET carbon beam irradiation may reduce radiation resistant nature originated from tumor hypoxia. In addition, hypo-fractionated irradiation of carbon beams showed successful local control in lung cancers. These results elucidates radio-biological advantages of the high LET particle therapy for cancer treatment.
