Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Phys Med Biol. 2011 Aug 7;56(15):4827-38. doi: 10.1088/0031-9155/56/15/013. Epub 2011 Jul 13.
A novel commercial medical linac system (TrueBeam™, Varian Medical Systems, Palo Alto, CA) allows respiratory-gated volumetric modulated arc therapy (VMAT), a new modality for treating moving tumors with high precision and improved accuracy by allowing for regular motion associated with a patient's breathing during VMAT delivery. The purpose of this work is to adapt a previously-developed dose reconstruction technique to evaluate the fidelity of VMAT treatment during gated delivery under clinic-relevant periodic motion related to patient breathing. A Varian TrueBeam system was used in this study. VMAT plans were created for three patients with lung or pancreas tumors. Conventional 6 and 15 MV beams with flattening filter and high-dose-rate 10 MV beams with no flattening filter were used in these plans. Each patient plan was delivered to a phantom first without gating and then with gating for three simulated respiratory periods (3, 4.5 and 6 s). Using the adapted log-file-based dose reconstruction procedure supplemented with ion chamber array (Seven29™, PTW, Freiburg, Germany) measurements, the delivered dose was used to evaluate the fidelity of gated VMAT delivery. Comparison of Seven29 measurements with and without gating showed good agreement with gamma-index passing rates above 99% for 1%/1 mm dose accuracy/distance-to-agreement criteria. With original plans as reference, gamma-index passing rates were 100% for the reconstituted plans (1%/1 mm criteria) and 93.5-100% for gated Seven29 measurements (3%/3 mm criteria). In the presence of leaf error deliberately introduced into the gated delivery of a pancreas patient plan, both dose reconstruction and Seven29 measurement consistently indicated substantial dosimetric differences from the original plan. In summary, a dose reconstruction procedure was demonstrated for evaluating the accuracy of respiratory-gated VMAT delivery. This technique showed that under clinical operation, the TrueBeam system faithfully realized treatment plans with gated delivery. This methodology affords a useful tool for machine- and patient-specific quality assurance of the newly available respiratory-gated VMAT.
一种新型商用医用直线加速器系统（TrueBeamTM，瓦里安医疗系统公司，帕洛阿尔托，加利福尼亚州）允许进行呼吸门控容积旋转调强弧形治疗（VMAT），这是一种通过允许与患者 VMAT 输送期间的呼吸相关的常规运动来治疗移动肿瘤的高精度和准确性提高的新方法。本工作的目的是开发一种以前开发的剂量重建技术，以评估与患者呼吸相关的临床相关周期性运动下门控输送期间 VMAT 治疗的保真度。本研究使用了瓦里安 TrueBeam 系统。为三名患有肺或胰腺肿瘤的患者创建了 VMAT 计划。在这些计划中，使用了常规的 6 和 15 MV 束以及带有平坦化滤波器的高剂量率 10 MV 束，而没有平坦化滤波器。每个患者计划首先在没有门控的情况下输送到一个体模中，然后在三个模拟呼吸周期（3、4.5 和 6 s）下进行门控输送。使用基于日志文件的经过修改的剂量重建过程，结合离子室阵列（Seven29TM，PTW，弗莱堡，德国）测量结果，使用输送剂量来评估门控 VMAT 输送的保真度。与没有门控的 Seven29 测量值进行比较，剂量精度/一致性距离的伽玛指数通过率大于 99%，达到 1%/1mm。对于原始计划作为参考，重新构建的计划（1%/1mm 标准）的伽玛指数通过率为 100%，门控 Seven29 测量值（3%/3mm 标准）的通过率为 93.5-100%。在胰腺患者计划的门控输送中故意引入叶片误差的情况下，剂量重建和 Seven29 测量均一致表明与原始计划存在显著的剂量差异。总之，已经证明了一种用于评估呼吸门控 VMAT 输送准确性的剂量重建过程。该技术表明，在临床操作下，TrueBeam 系统忠实地实现了门控输送的治疗计划。这种方法为新出现的呼吸门控 VMAT 的机器和患者特定质量保证提供了有用的工具。
