Patent ID: 8232536

Claim:
A particle beam irradiation system comprising: a particle beam generation part; a particle beam irradiation part where a charged particle beam that is generated in the particle beam generation part is irradiated on an irradiation target and; an irradiation control part that controls the charged particle beam to be irradiated; wherein the particle beam irradiation part comprises: a beam scanner that scans the charged particle beam laterally in two dimensions that is perpendicular to the irradiation direction of the charged particle beam; and a beam diameter changer that changes the beam diameter of the charged particle beam; wherein the irradiation control part comprises: an energy setting controller that sets the energy of the charged particle beam; a beam scanning controller that controls the beam scanner; and a beam diameter controller that controls the beam diameter changer; wherein the irradiation control part sets the beam diameter of the charged particle beam by the beam diameter controller to be a first beam diameter, the charged particle beam is scanned step-wise by the beam scanning controller so as to irradiate the charged particle beam on a predetermined region of the irradiation target, after that, the beam diameter of the charged particle beam is set by the beam diameter controller to be a second diameter that is different from the first beam diameter, and the charged particle beam is scanned step-wise by the beam scan controller so as to control the charged particle beam to irradiate on a region that is overlapped with at least a part of the predetermined part of the irradiation target.