Biological late effects for secondary radiations from carbon ions simulating clinical heavy-ion radiotherapy

Radiation-induced cancer is growing as one of the major concerns with the increasing number of patents surviving long time. Most current-particle radiotherapy is spread out the beams to cover the cancer using scattering and collimation systems, resulting in an extra whole-body irradiation from low dose secondary radiations, such as neutrons, protons and gamma rays. It is indeed observed in many secondary radiations from a carbon-ion track simulated by the Monte Carlo methods. We examined gene mutation at the HPRT locus as one of the indicators for late biological effects in normal human cells irradiated with low-fluence neutrons from an 241Am-Be source. The mutation frequency in the cells induced by 200kV X-ray challenging dose was reduced at 0.15 times in the cells pretreated with low-dose-rate neutrons (1mGy/8h) compared to non-pretreated cells, but the reduced mutation frequency was returned to the control level, when using a specific inhibitor of gap-junction mediated cell-cell communication. The result suggested that neutron-induced adaptive response was induced by gap-junction mediated bystander effect. (This is the co-operative study with Drs. T. Konishi and H. Kitamura.)第73回日本癌学会学術総