Patent Number: 
Section: claims

1. A rotating gantry that is equipped with a particle beam irradiation apparatus that irradiates a charged particle beam onto an irradiation subject and that can rotate around an isocenter,wherein a shielding material that attenuates a leakage dose of a secondary radiation generated by collision of the charged particle beam with the irradiation subject is provided at a position that is situated at the side opposed to the particle beam irradiation apparatus with respect to the irradiation subject and through which a beam axis of the charged particle beam is obstructed during irradiation, said beam axis being an axis that passes through a center line of the charged particle beam, andwherein the shielding material is disposed in such a way that when the irradiation subject does not exist in the rotating gantry, a portion of the shielding material that intersects the beam axis of the charged particle beam, is attachable and detachable, or can move in a sliding manner and in the rotation-axle direction of the rotating gantry to prevent obstruction, by the shielding material, of the beam axis and to enable ascertainment of the isocenter and a floor reference mark. 2. The rotating gantry according to claim 1, wherein there is provided a shielding material moving apparatus that moves the shielding material in the sliding manner and in the rotation-axle direction of the rotating gantry in such a way that the shielding material intersects the beam axis of the charged particle beam or departs from the beam axis. 3. The rotating gantry according to claim 1,wherein the shielding material includes a foundation portion fixed with respect to the beam axis of the charged particle beam and a detachable portion that is the beam axis portion and that is attachable and detachable, andwherein the shielding material is disposed in such a way that the detachable portion thereof intersects the beam axis of the charged particle beam. 4. The rotating gantry according to claim 3, wherein the shielding material includes a step-like engagement portion where the foundation portion and the detachable portion engage with each other. 5. The rotating gantry according to claim 3,wherein the shielding material includes an engagement portion where the foundation portion and the detachable portion engage with each other, andwherein when the engagement portion includes a beam axis parallel engagement portion where the foundation portion and the detachable portion engage with each other in a direction parallel to the beam axis, no portion of the beam axis parallel engagement portion defines a length that accounts for at least half of the length of the shielding material in the direction parallel to the beam axis. 6. The rotating gantry according to claim 3, wherein the material of the detachable portion is different from that of the foundation portion. 7. A particle beam therapy system comprising:a beam generation apparatus that generates a charged particle beam and accelerates the charged particle beam by means of an accelerator;a beam transport system that transports the charged particle beam accelerated by the accelerator;a particle beam irradiation apparatus that irradiates the charged particle beam transported by the beam transport system onto an irradiation subject; anda rotating gantry that is equipped with the particle beam irradiation apparatus and can rotate around the isocenter, wherein the rotating gantry is according to claim 1.