Wu J, Fahimian B, Wu H, Xing L
Purdue University, West Lafayette, IN.
Stanford University School of Medicine, Stanford, CA.
Med Phys. 2012 Jun;39(6Part24):3909. doi: 10.1118/1.4735957.
Gated Volumetric Modulated Arc Therapy (VMAT) is an emerging treatment modality for Stereotactic Body Radiotherapy (SBRT). However, gating significantly prolongs treatment time. In order to enhance treatment efficiency, a novel dual gated VMAT, in which dynamic arc deliveries are executed sequentially in alternating exhale and inhale phases, is proposed and evaluated experimentally.
The essence of dual gated VMAT is to take advantage of the natural pauses that occur at inspiration and exhalation by alternatively delivering the dose at the two phases, instead of the exhale window only. The arc deliveries at the two phases are realized by rotating gantry forward at the exhale window and backward at the inhale in an alternative fashion. Custom XML scripts were developed in Varian's TrueBeam STx Developer Mode to enable dual gated VMAT delivery. RapidArc plans for a lung case were generated for both inhale and exhale phases. The two plans were then combined into a dual gated arc by interleaving the arc treatment nodes of the two RapidArc plans. The dual gated plan was delivered in the development mode of TrueBeam LINAC onto a motion phantom and the delivery was measured by using pinpoint chamber/film/diode array (delta 4). The measured dose distribution was compared with that computed using Eclipse AAA algorithm. The treatment delivery time was recorded and compared with the corresponding single gated plans.
Relative to the corresponding single gated delivery, it was found that treatment time efficiency was improved by 95.5% for the case studied here. Pinpoint chamber absolute dose measurement agreed the calculation to within 0.7%. Diode chamber array measurements revealed that 97.5% of measurement points of dual gated RapidArc delivery passed the 3% and 3mm gamma-test criterion.
A dual gated VMAT treatment has been developed and implemented successfully with nearly doubled treatment delivery efficiency.
门控容积调强弧形放疗（VMAT）是立体定向体部放疗（SBRT）中一种新兴的治疗方式。然而，门控会显著延长治疗时间。为提高治疗效率，本文提出并通过实验评估了一种新型双门控VMAT，即在呼气和吸气阶段交替顺序执行动态弧形照射。
双门控VMAT的核心是利用吸气和呼气时的自然停顿，在两个阶段交替给予剂量，而非仅在呼气窗口给药。两个阶段的弧形照射通过在呼气窗口使机架向前旋转、在吸气时向后旋转来实现。在瓦里安TrueBeam STx开发者模式下开发了自定义XML脚本，以实现双门控VMAT照射。针对一个肺部病例，分别生成吸气和呼气阶段的RapidArc计划。然后通过交错两个RapidArc计划的弧形治疗节点，将这两个计划合并为一个双门控弧形计划。双门控计划在TrueBeam直线加速器的开发模式下施用于运动模体，并使用针点电离室/胶片/二极管阵列（delta 4）测量照射情况。将测量得到的剂量分布与使用Eclipse AAA算法计算的结果进行比较。记录治疗照射时间，并与相应的单门控计划进行比较。
相对于相应的单门控照射，发现本研究病例的治疗时间效率提高了95.5%。针点电离室绝对剂量测量结果与计算值的偏差在0.7%以内。二极管电离室阵列测量表明，双门控RapidArc照射97.5%的测量点通过了3%和3毫米的伽马测试标准。
已成功开发并实施了双门控VMAT治疗，治疗照射效率几乎提高了一倍。
