PROBLEM TO BE SOLVED: To improve dose distribution of charged particle beams in a peripheral edge part of an irradiation field while preventing an increase in a size of an irradiation nozzle in a charged particle beam treatment device that carries out scanning irradiation.SOLUTION: A multi-leaf collimator 30 of a charged particle beam treatment device 1 includes a pair of leaf groups 31 and 32 provided opposed to each other with a reference axis A of charged particle beams in between. The leaf groups 31 and 32 include a plurality of leaves 41 lined up in an X- direction, which can independently advance and retreat in a Y-direction, and block the charged particle beams, and a leaf driving part 43 for causing the leaves 41 to advance and retreat in the Y-direction. The length in the Y-direction of at least part of the plurality of leaves 41 is shorter than half of the length in the Y-direction of the maximum scanning scope.SELECTED DRAWING: Figure 2COPYRIGHT: (C)2018,JPO&INPIT【課題】スキャニング照射を行う荷電粒子線治療装置において、照射ノズルの大型化を防ぎつつ照射野の周縁部における荷電粒子線の線量分布を改善する。【解決手段】荷電粒子線治療装置1のマルチリーフコリメータ30は、荷電粒子線の基準軸Aを挟むように対向して設けられた一対のリーフ群31,32を有し、リーフ群31,32、X方向に複数並べられていると共に、Y方向に独立して進退可能であり、荷電粒子線を遮蔽するリーフ41と、リーフ41をY方向に進退させるリーフ駆動部43を、を有し、複数のリーフ41のうちの少なくとも一部は、Y方向における長さが、最大走査範囲のY方向における長さの半分よりも短い。【選択図】図2
