现代放射治疗用的电子直线加速器,~(60)钴治疗机及模拟定位机等都设等中心机构,即将机架、照射头和治疗床的三个旋转轴交于一点,称为等中心点(见图1)。将肿瘤置于等中心处进行放射治疗的方法称为等中心治疗。在放疗时,按机架的运动方式分为固定照射和旋转照射两种。一般临床上 Modern linear electron accelerators for radiation therapy, ~(60) cobalt therapy machines, and analog positioners are all equipped with isocenters. The three axes of rotation of the gantry, the irradiation head and the treatment bed are intersected at one point, called the isocenter. (see picture 1). The method of placing the tumor at the isocenter for radiotherapy is called isocenter treatment. In radiotherapy, the motion of the gantry can be divided into fixed and rotary irradiation. General clinical