Abstract

Water decomposition was observed for the first time from the gas evolution of Ra aqueous solution in 1901. However, it was observed that water is not decomposed by X-rays irradiation in 1920s. These findings were in contradiction and radiation chemists recognized the LET effect: different LET radiations have different radiation effects. Up to now, radiolysis of water with different ion beams has been clarified.

Radiation therapy is widely applied to cancer treatment and now ion beam radiation therapy is rapidly expanded. Advantages of ion beam radiation therapy will be discussed and, then, numbers of proton and carbon ion beam facilities for radiation therapy in Japan and in the world will be compared. In addition to heavy ion beam radiation therapy, boron neutron capture therapy (BNCT) in Japan will be briefly discussed.