VMAT optimization with dynamic collimator rotation.
VMAT optimization with dynamic collimator rotation.
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DOI：
10.1002/mp.12915
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发表时间：
2018-06
期刊：
影响因子：
3.8
通讯作者：
Sheng K
中科院分区：
文献类型：
--
作者：
Lyu Q;O'Connor D;Ruan D;Yu V;Nguyen D;Sheng K
尽管准直旋转是一个优化变量，可以探索用于剂量的优势，但现有的体积调制电弧疗法（VMAT）优化使用了每个弧中的固定准仪角度，并且在本研究中仅旋转弧形。 VMAT的方法，在弧运动过程中考虑动态直接仪角度。
通过添加到现有的剂量保真物镜中，可以实现用于VMAT（DC-VMAT）动态准直仪的直接孔径优化（DAO）用于控制每个光束角度的准直仪角当前的迭代和边缘成本占多叶准直仪的机械约束（MLC）。在具有两个小的球形靶标，一个大脑，肺和前列腺癌患者的幻影上测试了动态直接旋转。在患者研究中使用三个具有60度的准直仪角度分离的完整弧。
在相同的目标覆盖范围内，DC-VMAT在幻影研究中降低了R50的20.3％，并且与SC-VMAT相比，在患者研究中，平均最大和平均OAR剂量下降了4.49％和2.53％的处方剂量。与DC-VMAT计划中的龙门旋转协调的直接旋转计划在单ARC-DC-VMAT计划中有13个光束角度在患者研究中需要较慢的龙门旋转多个直接仪角度。
新型的DC-VMAT方法在弧传递过程中利用动态直接旋转，具有单个弧线的DC-VMAT可以实现比具有三个完整弧的SC-VMAT实现优质的剂量法。
Although collimator rotation is an optimization variable that can be exploited for dosimetric advantages, existing Volumetric Modulated Arc Therapy (VMAT) optimization uses a fixed collimator angle in each arc and only rotates the collimator between arcs. In this study, we develop a novel integrated optimization method for VMAT, accounting for dynamic collimator angles during the arc motion. Direct Aperture Optimization (DAO) for Dynamic Collimator in VMAT (DC-VMAT) was achieved by adding to the existing dose fidelity objective an anisotropic total variation term for regulating the fluence smoothness, a binary variable for forming simple apertures, and a group sparsity term for controlling collimator rotation. The optimal collimator angle for each beam angle was selected using the Dijkstra’s algorithm, where the node costs depend on the estimated fluence map at the current iteration and the edge costs account for the mechanical constraints of multi-leaf collimator (MLC). An alternating optimization strategy was implemented to solve the DAO and collimator angle selection (CAS). Feasibility of DC-VMAT using one full-arc with dynamic collimator rotation was tested on a phantom with two small spherical targets, a brain, a lung and a prostate cancer patient. The plan was compared against a static collimator VMAT (SC-VMAT) plan using three full arcs with 60 degrees of collimator angle separation in patient studies. With the same target coverage, DC-VMAT achieved 20.3% reduction of R50 in the phantom study, and reduced the average max and mean OAR dose by 4.49% and 2.53% of the prescription dose in patient studies, as compared with SC-VMAT. The collimator rotation coordinated with the gantry rotation in DC-VMAT plans for deliverability. There were 13 beam angles in the single-arc DC-VMAT plan in patient studies that requires slower gantry rotation to accommodate multiple collimator angles. The novel DC-VMAT approach utilizes the dynamic collimator rotation during arc delivery. In doing so, DC-VMAT affords more sophisticated intensity modulation, alleviating the limitation previously imposed by the square beamlet from the MLC leaf thickness and achieves higher effective modulation resolution. Consequently, DC-VMAT with a single arc manages to achieve superior dosimetry than SC-VMAT with three full arcs.
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