Patent Number: 
Section: abstract

A particle beam irradiation system capable of ensuring a more uniform dose distribution at an irradiation object even when a certain time is required from output of a beam extraction stop signal to the time when extraction of a charged particle beam from an accelerator is actually stopped. The particle beam irradiation system comprises a synchrotron, an irradiation device including scanning magnets and outputting an ion beam extracted from the synchrotron, and a control unit. The control unit stops the output of the ion beam from the irradiation device in accordance with the beam extraction stop signal, controls the scanning magnets to change an exposure position in a state in which the output of the ion beam is stopped, and after the change of the exposure position, starts the output of the ion beam from the irradiation device again. The control unit further outputs a next beam extraction stop signal when an increment of dose integrated from the time of a preceding beam extraction stop signal as a start point reaches a setting dose stored in advance.