Patent Number: 
Section: claims

1. A particle beam irradiation chamber in which a passage having a first opening part at the side of an inner wall and a second opening part at the side of an outer wall is provided, an isocenter is provided inside the particle beam irradiation chamber,wherein a first line segment which connects the center of the first opening part and the center of the second opening part does not intersect two side walls constituting the passage, when a vector which starts from the isocenter to the center of the first opening part is designated as a first vector and a vector which starts from the center of the first opening part to the center of the second opening part is designated as a second vector, a component of the first vector which is parallel to a line segment which connects both ends of the first opening part and a component of the second vector which is parallel to a line segment which connects both ends of the first opening are in an opposite direction, andθ is an angle larger than 0 degree and smaller than 90 degrees and is an angle which satisfies (a*sin θ+b*cos θ−t)cos θ>b−t,where a is a length of a perpendicular line which starts from the isocenter to a straight line E which connects both ends of the first opening part, b is a length of a perpendicular line which starts from the isocenter to a straight line F which is perpendicular to the straight line E, and passes a point which is farther away from the isocenter among points of both ends of the first opening part, t is a width of the passage, and θ is an angle which is formed by the straight line F and inner wall of the passage. 2. The particle beam irradiation chamber according to claim 1,wherein among two side walls constituting the passage, at least one side wall, from the first opening part to the second opening part, is constituted by a plurality of surfaces. 3. The particle beam irradiation chamber according to claim 1,wherein among two side walls constituting the passage, at least one side wall, from the first opening part to the second opening part, is constituted by a curved surface. 4. The particle beam irradiation chamber according to claim 1,wherein the isocenter is the rotation center of a rotary gantry device with which a particle beam irradiation nozzle is equipped, and the first opening part is not on a plane surface which passes the isocenter and is perpendicular to an axis of rotation of the rotary gantry device. 5. The particle beam irradiation chamber according to claim 1,wherein the isocenter is the rotation center of a rotary gantry device with which a particle beam irradiation nozzle is equipped, and a straight line, which is parallel to an axis of rotation of the rotary gantry device and starts from the isocenter and is extended to a passage side, intersects the first line segment in the passage. 6. The particle beam irradiation chamber according to claim 1,wherein a gateway of a positioning chamber is arranged in a position opposing the second opening part. 7. The particle beam irradiation chamber according to claim 1,wherein θ is an angle between 15 degrees and 30 degrees.