Department of Medical Physics and Radiotherapy, Casa di Cura S. Chiara, Piazza Indipendenza 11, 50129 Firenze, Italy.
Med Phys. 2011 Feb;38(2):612-21. doi: 10.1118/1.3533900.
To compare and evaluate different dosimetric techniques and devices for the QA of VMAT plans created by two treatment planning systems (TPSs).
A total of 50 VMAT plans were optimized for treatment of anatomical sites of various complexities by two TPSs which use rather different approaches to VMAT optimization. Dosimetric plan verifications were performed both as part of commissioning and as patient specific QA of clinical treatments. Absolute point doses were measured for all plans by a micro ion chamber inserted in a dedicated water-filled cylindrical phantom. Delivered dose distributions were verified by four techniques based on different detectors: radiographic and gafchromic films, two systems based on 2D diode arrays and an ion chamber array. Gamma index analysis with various tolerance levels (3%, 3 mm and 3%, 2 mm) was used to analyze differences between calculated and delivered doses. Sensitivity to possible delivery errors was also evaluated for three of the considered devices introducing +/-3 mm shifts along the three directions and a 3 degrees gantry offset.
Ion chamber measured point doses were within 3% of calculated ones for 48 out of 50 values. For delivered dose distribution, the average fraction of passed gamma values using 3% and 3 mm criteria was above 95% for both TPSs and all detectors except gafchromic film which yielded on average of 91.4%. For 49 out of 50 plans, a pass-rate above 94% was obtained by at least one of the four techniques. Shrinking the tolerance to 3% and 2 mm, the average pass-rate by all detectors (except film) was still above 95% for one of the two TPSs, but lower for the other one. The detector sensitivity to 3 mm shifts and to gantry angle offset was strongly plan and partially detector dependent: the obtained pass-rate reduction ranged from 2% to 30%.
The presented results for VMAT plans QA assess the reliability of the delivered doses for both TPSs. The slightly lower pass-rate obtained for one of the considered TPS can be attributed to a higher level of complexity of the optimized plans. The results by different dosimetric techniques are coherent, apart from a few measurements by gafchromic films. The detector sensitivity to delivery errors, being strongly plan dependent, is not easy to evaluate.
比较和评估两种治疗计划系统（TPS）创建的容积旋转调强（VMAT）计划的不同剂量学技术和设备，并对其进行评估。
使用两种TPS 优化了来自不同解剖部位的 50 个 VMAT 计划，这两种 TPS 采用了截然不同的 VMAT 优化方法。在计划制定和临床治疗的特定患者质量保证（QA）过程中，均进行了剂量学计划验证。使用插入专用充水圆柱体模中的微离子室，对所有计划进行了绝对点剂量测量。基于不同的探测器，采用了四种技术来验证实际剂量分布：放射性照相和 Gafchromic 胶片、基于二维二极管阵列和离子室阵列的两个系统。使用不同容差水平（3%、3mm 和 3%、2mm）的伽马指数分析，分析了计算剂量与实际剂量之间的差异。还对三种考虑的设备的敏感性进行了评估，这些设备沿三个方向引入了 +/-3mm 的偏移量和 3 度的机架偏移量。
对于 50 个值中的 48 个值，微离子室测量的点剂量与计算剂量相差在 3%以内。对于实际剂量分布，使用 3%和 3mm 标准时，两种 TPS 和所有探测器的通过伽马值的分数平均值均高于 95%，除了 Gafchromic 胶片，其平均值为 91.4%。对于 50 个计划中的 49 个计划，至少有一种技术的通过率超过 94%。将容差缩小到 3%和 2mm 时，两种 TPS 中除胶片外，所有探测器的平均通过率仍高于 95%，但另一个 TPS 的通过率较低。探测器对 3mm 偏移量和机架角度偏移的灵敏度强烈依赖于计划，部分依赖于探测器：获得的通过率降低范围从 2%到 30%。
对两种 TPS 的 VMAT 计划 QA 的结果评估了实际剂量的可靠性。对于考虑的 TPS 之一，获得的通过率略低，这可以归因于优化计划的复杂度更高。不同剂量学技术的结果是一致的，除了 Gafchromic 胶片的几次测量结果。由于计划依赖性很强，探测器对实际剂量误差的灵敏度不易评估。
