Pokhrel Damodar, Palmiero Allison N, Bernard Mark E, Clair William St
Department of Radiation Medicine, University of Kentucky, Lexington KY.
Department of Radiation Medicine, University of Kentucky, Lexington KY.
Med Dosim. 2021;46(2):195-200. doi: 10.1016/j.meddos.2020.11.005. Epub 2020 Dec 8.
Multiple small beamlets in the delivery of highly modulated single-isocenter HyperArc VMAT plan can lead to dose delivery errors associated with small-field dosimetry, which can be a major concern for stereotactic radiosurgery for multiple brain lesions. Herein, we describe and compare a clinically valuable dynamic conformal arc (DCA)-based VMAT (DCA-VMAT) approach for stereotactic radiosurgery of multiple brain lesions using flattening filter free beams to minimize this effect. Original single-isocenter HyperArc style VMAT and DCA-VMAT plans were created on 7 patients with 2 to 8 brain lesions (total 35 lesions) for 10 MV- flattening filter free beam. 20 Gy was prescribed to each lesion. For identical planning criteria, DCA-VMAT utilizes user-controlled field aperture shaper before VMAT optimization. Plans were evaluated for conformity and target coverage, low- and intermediate dose spillages to brain volume that received more than 30% (V30%) and 50% (V50%) of prescription dose. Additionally, mean brain dose, V8, V12 and maximal dose to adjacent organs-at-risk (OAR) including hippocampi were reported. Total monitor units, beam modulation factor, treatment delivery efficiency, and accuracy were recorded. Comparing with original VMAT, DCA-VMAT plans provided similar tumor dose, target coverage and conformity, yet tighter radio-surgical dose distribution with lower dose to normal brain V30% (p = 0.009), V50% (p = 0.05) and other OAR including lower dose to hippocampi. Lower total number of monitor units and smaller beam modulation factor reduced beam on time by 2.82 min (p < 0.001), on average (maximum up to 3.8 min). Beam delivery accuracy was improved by 8%, on average (p < 0.001) and maximum up to 13% in some cases for DCA-VMAT plans. This novel DCA-VMAT approach provided excellent plan quality, reduced dose to normal brain, and other OAR while significantly reducing beam-on time for radiosurgery of multiple brain lesions-improving patient compliance and clinic workflow. It also provided less MLC modulation through the targets-potentially minimizing small field dosimetry errors as demonstrated by quality assurance results. Incorporating DCA-based VMAT optimization in HyperArc module for radiosurgery of multiple brain lesions merits future investigation.
在高度调制的单等中心HyperArc容积调强放疗（VMAT）计划的实施过程中，多个小射束可能会导致与小射野剂量学相关的剂量传递误差，这对于多脑转移瘤的立体定向放射外科治疗来说可能是一个主要问题。在此，我们描述并比较了一种基于动态适形弧（DCA）的VMAT（DCA-VMAT）方法，该方法采用无均整器射束用于多脑转移瘤的立体定向放射外科治疗，以尽量减少这种影响。我们为7例患有2至8个脑转移瘤（共35个病灶）的患者创建了原始的单等中心HyperArc式VMAT和DCA-VMAT计划，使用10MV无均整器射束。每个病灶的处方剂量为20Gy。对于相同的计划标准，DCA-VCCA-VMAT在VMAT优化之前利用用户控制的射野孔径整形器。评估计划的适形度和靶区覆盖情况，以及对接受超过30%（V30%）和50%（V50%）处方剂量的脑体积的低剂量和中剂量溢出情况。此外，还报告了平均脑剂量、V8、V12以及包括海马体在内的相邻危及器官（OAR）的最大剂量。记录总监测单位、射束调制因子、治疗实施效率和准确性。与原始VMAT相比，DCA-VMAT计划提供了相似的肿瘤剂量、靶区覆盖和适形度，但放射外科剂量分布更紧密，对正常脑的V30%（p = 0.009）、V50%（p = 0.05）和其他OAR的剂量更低，包括对海马体的剂量更低。总监测单位数量减少，射束调制因子更小，平均射束开启时间减少了2.82分钟（p < 0.001）（最多可达3.8分钟）。DCA-VMAT计划的射束传递准确性平均提高了8%（p < 0.001），在某些情况下最高可达13%。这种新的DCA-VMAT方法提供了优异的计划质量，降低了对正常脑和其他OAR的剂量，同时显著减少了多脑转移瘤放射外科治疗的射束开启时间，提高了患者的依从性和临床工作流程。它还减少了通过靶区的多叶准直器调制，如质量保证结果所示，可能将小射野剂量学误差降至最低。将基于DCA的VMAT优化纳入HyperArc模块用于多脑转移瘤的放射外科治疗值得未来研究。
