准直器角度误差对脑转移瘤VMAT计划Gamma通过率的影响

【摘要】目的:通过旋转准直器角度模拟准直器角度误差，探讨准直器角度误差对单中心多发脑转移瘤容积旋转调强技术（VMAT）计划Gamma通过率的影响。方法:随机选取21例多发脑转移瘤患者的非共面VMAT计划，以无准直器角度误差放疗计划为模板计划，分别将准直器的角度旋转偏移±0.5°、±1.0°、±1.5°、±2.0°，不进行通量优化，重新计算剂量分布形成模拟计划，利用OmniPro-I’mRT软件比较模板计划与模拟计划在3%/3 mm、2%/3 mm、3%/2 mm、2%/2 mm及1%/1 mm标准下的Gamma通过率，并通过非参数配对Wilcoxon秩和检验分析不同准直器角度误差Gamma通过率的差异。结果:在3%/3 mm、2%/3 mm、3%/2 mm、2%/2 mm及1%/1 mm标准下，当准直器角度误差大于0.5°时，其Gamma通过率差异具有统计学意义（P<0.05）。在1%/1 mm标准下，-2.0°、-1.5°、-1.0°、-0.5°、0.5°、1.0°、1.5°、2.0°准直器角度误差的Gamma平均通过率分别降低4.80%、3.30%、2.00%、0.82%、0.73%、1.50%、2.10%和3.10%（P=0.003、0.005、0.020、0.593、0.469、0.043、0.030、0.001）。结论:随着准直器角度误差越大和应用标准越严格，Gamma通过率下降越大。为了保证VMAT计划执行的准确性，需要对准直器角度做更加严格的质量控制和保证控制，建议准直器角度误差控制在±0.5°范围内。

Effects of collimator angle error on Gamma passing rates for volumetric modulated arc therapy plan for intracranial metastases

Abstract: Objective To analyze the effect of collimator angle error which was simulated by rotating collimator angles on Gamma passing rates for volumetric modulated arc therapy (VMAT) plan for monocentric and multiple intracranial metastases. Methods The non-coplanar VMAT treatment plans of 21 patients with multiple intracranial metastases were analyzed. The radiotherapy plan without collimator angle error was taken as template plan, and then simulation plans were created by recalculating dose profiles without flux optimization after the collimator was rotated by ±0.5°, ±1.0°, ±1.5° and ±2.0°. OmniPro-I’mRT software was used to compare the Gamma passing rates between the template plan and simulation plans under the criteria of 3%/3 mm, 2%/3 mm, 3%/2 mm, 2%/2 mm and 1%/1 mm. The differences in Gamma passing rates of different collimator angles were analyzed by non-parametric paired Wilcoxon rank test. Results Under the criteria of 3%/3 mm, 2%/3 mm, 3%/2 mm, 2%/2 mm and 1%/1 mm, there was statistical difference (P<0.05) in Gamma passing rates when the collimator angle error was greater than 0.5°. The plans with the collimator angle errors of -2.0°, -1.5°, -1.0°, -0.5°, 0.5°, 1.0°, 1.5° and 2.0° had the mean Gamma passing rates decreased by 4.80%, 3.30%, 2.00%, 0.82%, 0.73%, 1.50%, 2.10% and 3.10%, respectively (P=0.003, 0.005, 0.020, 0.593, 0.469, 0.043, 0.030, 0.001), under the criterion of 1%/1 mm. Conclusion With greater collimator angle errors and stricter criteria, the decrease in mean Gamma passing rate becomes larger. The strengthening of quality control and assurance on collimator angle is required to guarantee the accuracy of VMAT delivery and it is recommended that the collimator angle error should be controlled within ±0.5°.