Radiation therapy has played an indispensable role in cancer therapy since the world’s first radiation therapy for cancer patients in 1896, the year after Dr. Röntgen discovered X-rays. In addition, the physicochemical properties of nuclear power and radiation are widely used in our daily lives, including in the energy industry. On the other hand, there are still many unclear points in the biological response to radiation; these issues must be solved in order to improve the effect of radiotherapy, to elucidate mechanism underlying carcinogenesis, and to establish a strategy to appropriately deal with the event of a nuclear disaster.