Fahimian Benjamin, Wu Junqing, Wu Huanmei, Geneser Sarah, Xing Lei
Department of Radiation Oncology, Stanford University, Stanford, CA, USA.
Radiat Oncol. 2014 Sep 25;9:209. doi: 10.1186/1748-717X-9-209.
Gated Volumetric Modulated Arc Therapy (VMAT) is an emerging radiation therapy modality for treatment of tumors affected by respiratory motion. However, gating significantly prolongs the treatment time, as delivery is only activated during a single respiratory phase. To enhance the efficiency of gated VMAT delivery, a novel dual-gated VMAT (DG-VMAT) technique, in which delivery is executed at both exhale and inhale phases in a given arc rotation, is developed and experimentally evaluated.
Arc delivery at two phases is realized by sequentially interleaving control points consisting of MUs, MLC sequences, and angles of VMAT plans generated at the exhale and inhale phases. Dual-gated delivery is initiated when a respiration gating signal enters the exhale window; when the exhale delivery concludes, the beam turns off and the gantry rolls back to the starting position for the inhale window. The process is then repeated until both inhale and exhale arcs are fully delivered. DG-VMAT plan delivery accuracy was assessed using a pinpoint chamber and diode array phantom undergoing programmed motion.
DG-VMAT delivery was experimentally implemented through custom XML scripting in Varian's TrueBeam™ STx Developer Mode. Relative to single gated delivery at exhale, the treatment time was improved by 95.5% for a sinusoidal breathing pattern. The pinpoint chamber dose measurement agreed with the calculated dose within 0.7%. For the DG-VMAT delivery, 97.5% of the diode array measurements passed the 3%/3 mm gamma criterion.
The feasibility of DG-VMAT delivery scheme has been experimentally demonstrated for the first time. By leveraging the stability and natural pauses that occur at end-inspiration and end-exhalation, DG-VMAT provides a practical method for enhancing gated delivery efficiency by up to a factor of two.
门控容积调强弧形放疗（VMAT）是一种用于治疗受呼吸运动影响的肿瘤的新兴放疗方式。然而，门控会显著延长治疗时间，因为放疗仅在单个呼吸阶段进行。为提高门控VMAT放疗的效率，开发了一种新型双门控VMAT（DG-VMAT）技术，并进行了实验评估，该技术在给定的弧形旋转中，呼气和吸气阶段均进行放疗。
通过依次交错由呼气和吸气阶段生成的VMAT计划的MU、MLC序列和角度组成的控制点，实现两个阶段的弧形放疗。当呼吸门控信号进入呼气窗口时，启动双门控放疗；呼气放疗结束后，光束关闭，机架回滚到吸气窗口的起始位置。然后重复该过程，直到呼气和吸气弧形放疗均全部完成。使用经历编程运动的针点电离室和二极管阵列体模评估DG-VMAT计划放疗的准确性。
通过瓦里安TrueBeam™ STx开发者模式中的自定义XML脚本，对DG-VMAT放疗进行了实验实现。对于正弦呼吸模式，相对于呼气时的单门控放疗，治疗时间缩短了95.5%。针点电离室剂量测量结果与计算剂量的偏差在0.7%以内。对于DG-VMAT放疗，97.5%的二极管阵列测量结果通过了3%/3mm伽马标准。
首次通过实验证明了DG-VMAT放疗方案的可行性。通过利用吸气末和呼气末出现的稳定性和自然停顿，DG-VMAT提供了一种切实可行的方法，可将门控放疗效率提高一倍。
