Rotating gantry and particle beam therapy system

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, and

wherein 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, and

wherein 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, and

wherein 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; and

a 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 .