确定旋转放疗设备等中心点的平均矢量算法

Average vector method for determining isocenter of rotated radiotherapy equipment

对于旋转放射治疗设备,其等中心点位置对治疗精度存在重要影响。针对设备负载引起的机械结构变形对等中心误差的影响,提出了一种确定旋转放疗设备等中心点的平均矢量算法。以等中心点位置为优化变量,通过限定等中心点与不同位置射线向量的最大距离建立约束条件,以满足约束条件的等中心点与射线向量的平均距离为目标函数,得到最优等中心点位置和等中心包络线。实例分析验证了平均矢量算法的正确性和有效性。平均矢量法与矢量法得出的等中心包络线半径均为0.311mm,比节点法降低约15.5%;平均矢量法给出的等中心点距各射线向量的平均距离为0.206mm,比矢量法降低约11.2%,比节点法降低约28%。

The isocentric accuracy of rotated radiotherapy equipment significantly influences the treatment accuracy.The average vector method is used to find the optimal isocenter considering the mechanical deformation of the rotated radiotherapy equipment.The maximum distance between the isocenter which is treated as the optimization variable and the ray vectors is considered as a constraint.An objective function is then designed to calculate the average distance between the isocenter that meets the constraint and the ray vectors.Finally,the location of the optimal isocenter and the isocentric envelop are obtained.A test with this method gives the radius of the isocentric envelop as 0.311 mm which is equal to that given by the vector-end-effector method,and about 15.5%less than that given by the point-end-effector method.The results also show that the average distance between the optimal isocenter and the ray vectors is 0.206 mm, about 11.2% less than that by the vector-end-effector method and 28% less than that by the point-end-effector method.