机械旋转误差对多发脑转移瘤VMAT计划剂量分布的影响

目的:探讨直线加速器的机械旋转误差对单中心多发转移瘤VMAT计划剂量分布的影响。方法:随机选取21例多发脑转移瘤患者，假定患者均采用非共面VMAT放疗计划，分别将治疗床、准直器的角度旋转偏移±]0.5°、±]1.0°、±]1.5°、±]2.0°，并通过Eclipse 13.6治疗计划系统模拟机械旋转偏移误差在多发脑转移瘤VMAT计划中对剂量分布的影响。记录并分析不同治疗床、准直器角度旋转偏移下靶区的适形度指数（CI）、剂量梯度跌落指数（GI）、剂量均匀性指数（HI）以及危及器官的最大剂量。结果:当治疗床及准直器角度旋转偏移大于0.5°时，靶区的CI、GI（治疗床除外）及HI指数差异具有统计学意义（P<0.05）；危及器官的最大剂量差异无统计学意义（P>0.05）。结论:在设计多发脑转移VMAT计划时应考虑等中心与靶区之间的距离，六维床旋转误差校正阈值为0.5°更为合理。

Effect of rotational mechanical errors on dose distribution of volumetric modulated arc therapy for multiple intracranial metastases

Objective To investigate the effect of rotationalmechanical errors of linear accelerator on the dose distribution of singleisocenter volumetricmodulated arc therapy(VMAT)formultiple intracranialmetastases.MethodsAtotal of 21 patientswithmultiple intracranial metastases were enrolled in the study.Assuming that patients were treated with non-coplanarVMAT,the treatment couch and collimator angle were shifted by±0.5°,±1.0°,±1.5°and±2.0°,respectively.Eclipse 13.6 treatment planning system was used to study the effects of the rotational mechanical errors on dose distribution of VMAT for multiple intracranial metastases.With different rotational errors,the conformity index,gradient index and homogeneity index of target areas as well as the maximumdose of organs-at-risk were recorded and analyzed.Results There were significant differences in the conformity index,gradient index(except for couch),and homogeneity index of target areas(P<0.05)when the rotational deviations of treatment couch and collimator angle were greater than 0.5°.No significant difference was found in the maximum dose of organs-at-risk(P>0.05).Conclusion In the planning of VMAT for multiple intracranial metastases,the distance between the isocenter and target areas should be taken into consideration and the reasonable correction threshold for six-dimensional couch rotational errors should be 0.5°.