Department of Radiation Oncology and Molecular Radiation Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
Med Phys. 2010 Aug;37(8):4146-54. doi: 10.1118/1.3455286.
Volumetric modulated arc therapy (VMAT) is a rotational delivery technique in which MLC shapes, dose rate, and gantry rotation speed are optimized to produce conformal dose distributions. The aim of this work is to develop a beam projection method for deriving the optimal table and collimator angles for multilesion treatment planning.
The method consists of four steps. The first step is to define the vector of beam-eye-view (BEV)-Y-axis in the treatment planning CT coordinates. The second step is to project each target onto the BEV-Y-axis vector. In the third step, the best table and collimator angle are found with a brute-force optimization technique that minimizes MLC leaf sharing between lesions. The fourth step is to generate an optimized VMAT plan with appropriate table/collimator angles and evaluate the plan quality.
The authors tested the method on three example cases with targets of various locations in the brain and sizes ranging from 1.18 to 17.86 cm(3). Applying the optimized geometric parameter to generate VMAT plan, a reduction of the 12 Gy volume was more than 6.1% for all cases; the plan homogeneity (D2%-D95%) was improved from 5.88 +/- 1.21 to 5.21 +/- 0.93 Gy vs a VMAT plan with the manufacturer recommended table and collimator angles.
The authors conclude that the use of the projection method minimizes the sharing of MLC leaves between lesions and improves the plan quality for multilesion VMAT delivery.
容积调强弧形治疗（VMAT）是一种旋转式递送技术，其中通过优化多叶准直器形状、剂量率和机架旋转速度来产生适形剂量分布。本研究旨在开发一种用于多病灶治疗计划的束投影方法，以获得最佳的治疗床和准直器角度。
该方法包括四个步骤。第一步是在治疗计划 CT 坐标系中定义视线（BEV）-Y 轴的向量。第二步是将每个目标投影到 BEV-Y 轴向量上。第三步是通过最小化病灶之间的多叶准直器叶片共享来使用暴力优化技术找到最佳的治疗床和准直器角度。第四步是生成具有适当治疗床/准直器角度的优化 VMAT 计划，并评估计划质量。
作者在三个具有不同位置和大小（1.18 至 17.86 cm³）的脑部目标的示例病例中测试了该方法。应用优化的几何参数生成 VMAT 计划，所有病例的 12 Gy 体积减少均超过 6.1%；与使用制造商推荐的治疗床和准直器角度生成的 VMAT 计划相比，计划均匀性（D2%-D95%）从 5.88 +/- 1.21 提高到 5.21 +/- 0.93 Gy。
作者得出结论，使用投影方法可以最小化病灶之间的多叶准直器叶片共享，并提高多病灶 VMAT 递送的计划质量。
