| 摘要 |
PROBLEM TO BE SOLVED: To solve the former problem that, since the setting of a radiation field depends on an experience/skill of an operator of an apparatus, a rotation angle of a rotatable multi-leaf collimator can not be optimized. SOLUTION: The multistage multi-leaf collimator is equipped with a first and a second multi-leaf collimators 4 and 5 in which leaf groups respectively comprising two or more leaves with intervals in a radiation direction of a beam are disposed to face each other on a same plane and arbitrarily form the radiation fields to a radiation target in a direction perpendicular to the beam, and a rotation means to rotate the collimators 4 and 5 around a common axis in a direction of a beam optical axis, wherein areas of beam radiation fields which are formed by the duplication of the individual radiation fields, respectively formed by the leaf groups of the collimators 4 and 5 at the positions to be inscribed or circumscribed to the beam radiation target are calculated, the areas of the beam radiation fields at the arbitrary rotation positions set by the rotation means are compared, and the rotation position becoming the minimum area in the case of being inscribed or the rotation position becoming the maximum area in the case of being circumscribed is calculated as the optimum rotation angle. COPYRIGHT: (C)2006,JPO&NCIPI
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