Charged particle beam transport system and particle beam therapy system

A charged particle beam transport system that transports a charged particle beam to a particle beam irradiation apparatus mounted in a rotating gantry capable of rotating around an isocenter, the charged particle beam transport system comprising:

• a rotating deflection unit that is mounted in the rotating gantry and rotates around a gantry rotation axle of the rotating gantry;
• and
• a fixed transport unit ranging from an accelerator to the rotating deflection unit,
• wherein letting an x direction denote a direction on a circular orbit plane of the accelerator in a plane perpendicular to a traveling direction of the charged particle beam at a launching position of the accelerator and letting a y direction denote a direction perpendicular to the x direction in a plane perpendicular to the traveling direction of the charged particle beam, the charged particle beam launched from the accelerator is a charged particle beam whose x-direction and y-direction emittances are different from each other,
• wherein the rotating deflection unit includes two or more deflection electromagnets, the fixed transport unit includes two or more quadrupole electromagnets,
• wherein the fixed transport unit decides x-direction phase space distribution of the charged particle beam at an inlet of the rotating deflection unit by controlling excitation amounts of the quadrupole electromagnets,
• wherein the x-direction phase space distribution is a distribution that can be approximated with a linear distribution calculated by use of a predetermined selection matrix,
• wherein the selection matrix is part of a transport matrix over a section from the inlet of the rotating deflection unit to the isocenter in the case where at the inlet and an outlet of the rotating deflection unit, x-direction and y-direction momentum dispersion functions are 0 and a gradient of the traveling direction, of the charged particle beam, that is perpendicular to the x direction and the y direction in the momentum dispersion function is 0;
• and the selection matrix has transport matrix elements m11, m12, m33, and m34 that link a position (x1, y1) of a charged particle included in the charged particle beam at the inlet of the rotating deflection unit and a gradient (x′1, y′1) of the traveling direction of the charged particle beam at the inlet of the rotating deflection unit with a position (x2, y2) of the charged particle at the isocenter and a gradient (x′2, y′2) of the traveling direction of the charged particle beam at the isocenter, and
• wherein letting σy denote y-direction beam size at the isocenter, letting a first equation denote “m11x0+m12x′0=σy”, and letting a second equation denote “m33x0+m34x′0=σy”, one end point (x0, x′0) and the other end point (−x0, −x′0) of the linear distribution are calculated from the first and second equations.