To provide a method for optimizing an radiation treatment by a multi-leaf collimator so as to increase the life of the collimator or to reduce a treatment time.

Each leaf of the multi-leaf collimator which is positioned for blocking a radiation from a radiation source and deciding an opening between the radiation source and a treatment area fixes each treatment field and the fields are ordered in the method. In the method, the multi-leaf collimator is relatively rotated and operated concerning the treatment area in order to decide more than one treatment ports, collimator ports are relatively arrayed based on the mobile direction of the collimator concerning the treatment area so as to permit each port to have at least one adjacent port and the order of the treatment fields with respect to each collimator port is selected based on the treatment field in the adjacent port in order to optimize the supply of the radiation.