A radiation source can be released along the beam axis the beam of radiation therapy, the radiation therapy device is rotatable about a rotation axis substantially perpendicular to the beam axis, the axis whereby a multi-leaf collimator which consists of a source of an arc having a center, so as to collimate the desired shape of the beam, the rate of dose / time of the source, the rotation speed of the source, and the multi-leaf collimator and a control unit that can control the position. A treatment plan arc is divided into conceptual arc segments, the control means is configured to receive a treatment plan that specifies the start position and the end position of the MLC and the overall dose for the arc segment there. Control means is configured to control the radiation source according to the plan. During this segment of the first, one with a constant, multi-leaf collimator is made so as to change the shape of the dose rate at least rotation and speed. Also, it will be constant at different levels to a constant level during this second segment, wherein at least one dose rate and rotational speed, adopted by the arc of the first segment. A total time required by the arc segment, the MLC leaves moving at maximum leaf speed to the position at the end of the predetermined arc segments, such control, the arc from the position of the start of the predetermined arc segment calculated for several factors, including the rotation of the source at maximum ray source rotation speed from the beginning to the end of the segment, and a delivery of the dose in the dose rate per hour maximum, and, a factor that indicates the maximum time By picked, and to operate at its maximum speed for factor picked out, and controls the device to operate at reduced rate is selected to be compatible with the maximum time for factors remaining are realized.放射線治療装置は、治療用の放射線のビームをビーム軸線に沿って放出することができる線源であって、ビーム軸線と実質的に直交する回転軸線を中心として回転自在であり、これによって軸線を中心とした弧を描く線源と、前記ビームを所望の形状にコリメートするように構成された多分割コリメータと、線源の
