Duke University Medical Center, Durham, North Carolina 27710.
Med Phys. 2013 Dec;40(12):121725. doi: 10.1118/1.4829518.
Recent trends in stereotactic radiosurgery use multifocal volumetric modulated arc therapy (VMAT) plans to simultaneously treat several distinct targets. Conventional verification often involves low resolution measurements in a single plane, a cylinder, or intersecting planes of diodes or ion chambers. This work presents an investigation into the consistency and reproducibility of this new treatment technique using a comprehensive commissioned high-resolution 3D dosimetry system (PRESAGE(®)∕Optical-CT).
A complex VMAT plan consisting of a single isocenter but five separate targets was created in Eclipse for a head phantom containing a cylindrical PRESAGE(®) dosimetry insert of 11 cm diameter and height. The plan contained five VMAT arcs delivering target doses from 12 to 20 Gy. The treatment was delivered to four dosimeters positioned in the head phantom and repeated four times, yielding four separate 3D dosimetry verifications. Each delivery was completely independent and was given after image guided radiation therapy (IGRT) positioning using Brainlab ExacTrac and cone beam computed tomography. A final delivery was given to a modified insert containing a pin-point ion chamber enabling calibration of PRESAGE(®) 3D data to dose. Dosimetric data were read out in an optical-CT scanner. Consistency and reproducibility of the treatment technique (including IGRT setup) was investigated by comparing the dose distributions in the four inserts, and with the predicted treatment planning system distribution.
Dose distributions from the four dosimeters were registered and analyzed to determine the mean and standard deviation at all points throughout the dosimeters. A dose standard deviation of <3% was found from dosimeter to dosimeter. Global 3D gamma maps show that the predicted and measured dose matched well [3D gamma passing rate was 98.0% (3%, 2 mm)].
The deliveries of the irradiation were found to be consistent and matched the treatment plan, demonstrating high accuracy and reproducibility of both the treatment machine and the IGRT procedure. The complexity of the treatment (multiple arcs) and dosimetry (multiple strong gradients) pose a substantial challenge for comprehensive verification. 3D dosimetry can be uniquely effective in this scenario.
立体定向放射外科的最新趋势是使用多焦点容积调制弧形治疗（VMAT）计划同时治疗多个不同的靶区。传统的验证通常涉及在单个平面、圆柱体或相交的二极管或离子室平面中进行低分辨率测量。本工作使用经过全面委托的高分辨率 3D 剂量测定系统（PRESAGE®/Optical-CT）研究了这种新治疗技术的一致性和可重复性。
在 Eclipse 中为包含直径和高度为 11 厘米的圆柱形 PRESAGE®剂量测定插件的头部体模创建了一个复杂的 VMAT 计划，该计划由一个单中心点但五个单独的靶区组成。该计划包含五个 VMAT 弧形，以 12 至 20 Gy 的剂量输送靶区。对定位在头部体模中的四个剂量计进行四次治疗，每次重复四次，得到四个单独的 3D 剂量验证。每次交付都是完全独立的，并在使用 Brainlab ExacTrac 和锥形束计算机断层扫描进行图像引导放射治疗（IGRT）定位后进行。最后一次交付给一个经过修改的插件，其中包含一个针状离子室，使 PRESAGE®3D 数据能够校准剂量。在光学 CT 扫描仪中读取剂量计数据。通过比较四个插件中的剂量分布以及与预测的治疗计划系统分布，研究了治疗技术（包括 IGRT 设置）的一致性和可重复性。
对四个剂量计的剂量分布进行了注册和分析，以确定整个剂量计中所有点的平均值和标准偏差。从剂量计到剂量计发现剂量标准偏差<3%。全局 3D 伽马图显示，预测剂量与测量剂量匹配良好[3D 伽马通过率为 98.0%（3%，2 毫米）]。
照射的输送被发现是一致的，与治疗计划相匹配，证明了治疗机器和 IGRT 程序的高精度和可重复性。治疗的复杂性（多个弧形）和剂量测定（多个强梯度）对全面验证构成了重大挑战。3D 剂量测定在这种情况下可以是独特有效的。
