PROBLEM TO BE SOLVED: To provide a charged particle beam treatment apparatus capable of both improving the penumbra and ensuring the flatness of dose distribution. SOLUTION: The control unit irradiates a charged particle beam on a peripheral portion of an irradiation field 60 defined by the multi-leaf collimator 24 with a higher level than when irradiating the charged particle beam on another portion of the irradiation field 60. Modulate the dose of charged particle beam. Therefore, in the peripheral portion of the irradiation field 60, the dose of the charged particle beam itself is increased due to the modulation, so that the flatness of the dose distribution is reduced although the penumbra is improved, but the charged particle beam in the peripheral portion of the irradiation field is reduced. The dose distribution can be flattened by shielding a part of it with the multi-leaf collimator 24. [Selection diagram] Fig. 4【課題】ペナンブラの改善と、線量分布の平坦度の確保を両立することができる荷電粒子線治療装置を提供する。【解決手段】制御部は、マルチリーフコリメータ２４で規定された照射野６０の周縁部に荷電粒子線を照射するときは、照射野６０における他の部分に荷電粒子線を照射するときよりも高い線量の荷電粒子線に変調する。従って、照射野６０の周縁部では、変調によって荷電粒子線自体の線量が高くなっているためペナンブラが改善されながらも線量分布の平坦度が低下するが、照射野の周縁部の荷電粒子線の一部をマルチリーフコリメータ２４で遮蔽することで線量分布を平坦化させることができる。【選択図】図４
