Patent Number: 
Section: claims

1. A gantry type particle beam irradiation system which comprises a gantry and is configured such that a particle beam is extracted from a circular accelerator, in a case where a direction in a circular track plane of the circular accelerator is defined as X direction in a plane which is perpendicular to a travelling direction of the particle beam at an extraction position of the circular accelerator, and the direction which is perpendicular to X direction in a plane which is perpendicular to the travelling direction of the particle beam is defined as Y direction, the particle beam has small emittance in X direction and large emittance in Y direction, and the particle beam which is transported by a particle beam transportation unit is irradiated from an irradiation nozzle installed in the gantry to an irradiation target,wherein the irradiation nozzle has a ridge filter,an angle of the gantry, with which the particle beam is transported so as for emittance in X direction and emittance in Y direction at the extraction position of the circular accelerator to be separated and to maintain each emittance at a position where the particle beam is incident on the irradiation nozzle, is defined as a reference angle, in the state where the gantry is the reference angle the ridge filter is installed so as for the direction in which emittance in X direction is maintained is tilted to the direction which is perpendicular to a ridge of the ridge filter by a predetermined angle. 2. The particle beam irradiation system according to claim 1, wherein the predetermined angle is in a range of 20 degrees to 70 degrees. 3. The particle beam irradiation system according to claim 1, wherein the predetermined angle is 45 degrees. 4. The particle beam irradiation system according to claim 1, wherein the ridge filter has a rectangular base, and a direction which is perpendicular to a ridge of the ridge filter is tilted to a direction to which one side of the base extends by a predetermined angle. 5. The particle beam irradiation system according to claim 1,wherein the gantry has the configuration in which a plane which is formed by a center line of the particle beam which is deflected in the gantry is a flat plane, at an angle of the gantry in which the flat plane is perpendicular to the circular track plane of the circular accelerator, a direction in which emittance in the X direction of the particle beam in the irradiation nozzle is maintained is defined as a reference axis and the ridge filter is installed by tilting a direction which is perpendicular to a ridge of the ridge filter to a direction of the reference axis. 6. A particle beam therapy system comprising a circular accelerator, a particle beam transportation unit for transporting a particle beam which is extracted from the circular accelerator, a treatment table for laying a patient and a gantry-type particle beam irradiation system according to claim 1.