Snyder Jeffrey E, Fast Martin F, Uijtewaal Prescilla, Borman Pim T S, Woodhead Peter, St-Aubin Joël, Smith Blake, Shepard Andrew, Raaymakers Bas W, Hyer Daniel E
Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut; Department of Radiation Oncology, University of Iowa, Iowa City, Iowa.
Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
Int J Radiat Oncol Biol Phys. 2025 Jul 15;122(4):976-985. doi: 10.1016/j.ijrobp.2024.10.028. Epub 2024 Oct 26.
Long treatment sessions are a limitation within magnetic resonance imaging guided adaptive radiation therapy (MRIgART). This work aims for significantly enhancing the delivery efficiency on the magnetic resonance linear accelerator (MR-linac) by introducing dedicated optimization and delivery techniques for volumetric modulated arc therapy (VMAT). VMAT plan and delivery quality during MRIgART is compared with step-and-shoot intensity-modulated radiation therapy (IMRT) for prostate stereotactic body radiation therapy.
Ten patients with prostate cancer previously treated on a 1.5T MR-linac were retrospectively replanned to 36.25 Gy in 5 fractions using step-and-shoot IMRT and the clinical Hyperion optimizer within Monaco (Hyp-IMRT), the same optimizer with a VMAT technique (Hyp-VMAT), and a research-based optimizer called optimal fluence levels and pseudo gradient descent with VMAT (OFL+PGD-VMAT). The plans were then adapted onto each daily magnetic resonance imaging data set using 2 different optimization strategies to evaluate the adapt-to-position workflow: "optimize weights" (IMRT-Weights and VMAT-Weights) and "optimize shapes" (IMRT-Shapes and VMAT-Shapes). Treatment efficiency was evaluated by measuring optimization time, delivery time, and total time (optimization+delivery). Plan quality was assessed by evaluating organ at risk sparing. Ten patient plans were measured using a modified linac control system to assess delivery accuracy via a gamma analysis (2%/2 mm). Delivery efficiency was calculated as average dose rate divided by maximum dose rate.
For Hyp-VMAT and OFL+PGD-VMAT, the total time was reduced by 124 ± 140 seconds (P = .020) and 459 ± 110 seconds (P < .001), respectively, as compared with the clinical Hyp-IMRT group. Speed enhancements were also measured for adapt-to-position with reductions in total time of 404 ± 55 (P < .001) for VMAT-Weights as compared with the clinical IMRT-Shapes group. Bladder and rectum dosimetric volume histogram (DVH) points were within 1.3% or 0.8 cc for each group. All VMAT plans had gamma passing rates greater than 96%. The delivery efficiency of VMAT plans was 89.7 ± 2.7 % compared with 50.0 ± 2.2 % for clinical IMRT.
Incorporating VMAT into MRIgART will significantly reduce treatment session times while maintaining equivalent plan quality.
在磁共振成像引导的自适应放射治疗（MRIgART）中，较长的治疗时间是一个限制因素。本研究旨在通过引入用于容积调强弧形治疗（VMAT）的专用优化和交付技术，显著提高磁共振直线加速器（MR-linac）的交付效率。将MRIgART期间的VMAT计划和交付质量与用于前列腺立体定向体部放射治疗的静态调强放射治疗（IMRT）进行比较。
对10例先前在1.5T MR-linac上接受治疗的前列腺癌患者进行回顾性重新计划，使用静态IMRT和Monaco中的临床Hyperion优化器（Hyp-IMRT）、采用VMAT技术的相同优化器（Hyp-VMAT）以及一种基于研究的名为最佳注量水平和带VMAT的伪梯度下降（OFL+PGD-VMAT）的优化器，将剂量分割为5次，总剂量36.25 Gy。然后使用2种不同的优化策略将计划适配到每个每日磁共振成像数据集上，以评估适应位置工作流程：“优化权重”（IMRT-权重和VMAT-权重）和“优化形状”（IMRT-形状和VMAT-形状）。通过测量优化时间、交付时间和总时间（优化+交付）来评估治疗效率。通过评估危及器官的保留情况来评估计划质量。使用改良的直线加速器控制系统测量10例患者计划，通过伽马分析（2%/2 mm）评估交付准确性。交付效率计算为平均剂量率除以最大剂量率。
与临床Hyp-IMRT组相比，对于Hyp-VMAT和OFL+PGD-VMAT，总时间分别减少了124±140秒（P = 0.020）和459±110秒（P < 0.001）。与临床IMRT-形状组相比，VMAT-权重在适应位置时的速度也有所提高，总时间减少了404±55秒（P < 0.001）。每组膀胱和直肠的剂量体积直方图（DVH）点在1.3%或0.8 cc以内。所有VMAT计划的伽马通过率均大于96%。VMAT计划的交付效率为89.7±2.7%，而临床IMRT为50.0±2.2%。
将VMAT纳入MRIgART将显著减少治疗时间，同时保持相当的计划质量。
