New medical irradiation technique by the permanent magnet system for the heavy-ion therapy

A rotating gantry has been a popular tool for a radiation cancer therapy. However, the heavy-ion gantry is huge and expensive, because of the higher magnetic rigidity than that of a proton beam. As one of the downsizing methods, the field strength of a wobbling magnet for a uniform lateral-dose distribution should be increased. Since the field strength of the conventional wobbler is limited by an eddy-current effect under an operation frequency of around 50 Hz, we propose a new wobbling technique by rotating a pair of permanent magnets with a high magnetic field of around 2 T. For carbon-ion therapy, the proposed technique reduces the irradiation-port length considerably to around 2 m from more than 6 m in the conventional-gantry design.