A comprehensive formulation for volumetric modulated arc therapy planning
A comprehensive formulation for volumetric modulated arc therapy planning
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DOI：
10.1118/1.4953832
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发表时间：
2016-07-01
期刊：
影响因子：
3.8
通讯作者：
Sheng, Ke
中科院分区：
文献类型：
--
作者：
Nguyen, Dan;Lyu, Qihui;Sheng, Ke
目的：体积调制电弧治疗（VMAT）是一种广泛应用的放射治疗技术，具有与静态光束强度调制放射治疗（IMRT）相当的剂量学，减少了监测单元和治疗时间。然而，目前的VMAT优化采用了各种贪婪的启发式算法来求解经验解，从而影响了方案的一致性和质量。为了克服这些限制，作者提出了一种新的直接孔径优化方法。方法：将VMAT （comVMAT）综合规划制定为一个优化问题，其中包含l2范数保真度项以补偿优化剂量与规定剂量之间的差异，以及各向异性总变差项以促进影响图的分段连续性，为直接孔径优化做好准备。采用水平集函数描述孔径形状，并对相邻角度孔径形状的差异进行惩罚，控制MLC的运动范围。采用近类优化求解器求解大规模优化问题，采用交替优化策略同时求解影响强度和孔径形状。单弧通信计划，利用180梁与2。为多形性胶质母细胞瘤病例，肺（LNG）病例和两个头颈部病例-一个有三个ptv （H&N-3PTV）和一个有四个ptv (h&n4ptv)-生成角分辨率，以测试疗效。采用交替优化策略对方案进行优化。将该方案与临床VMAT （clnVMAT）方案进行比较，该方案采用两个重叠的共面弧线进行治疗。结果：在块最小化算法的600次迭代内，comVMAT方案的优化得到收敛。与clnVMAT计划相比，comVMAT计划能够持续减少对所有危险器官（OARs）的剂量。平均而言，commmat方案使最大OAR剂量和平均OAR剂量分别比处方剂量降低6.59%和7.45%。LNG病例的最大剂量和平均剂量降低高达14.5 Gy， H&N-3PTV病例的最大剂量和平均剂量降低高达15.3 Gy。D95、D98、D99测定的PTV覆盖率均在处方剂量的0.25%以内。通过全面优化所有光束，commmat优化器获得了允许某些选定光束提供更高强度的自由，产生的剂量分布类似于具有光束方向优化的静态光束IMRT计划。结论：新型的非贪婪VMAT方法同时优化了弧形内的所有光束，然后直接产生可交付的孔径。因此，单弧VMAT方法充分利用了数字直线加速器在剂量率和龙门转速调制方面的能力。在实践中，新的单VMAT算法生成的方案优于现有的利用两个弧线的VMAT算法。(C) 2016年美国医学物理学家协会。
Purpose: Volumetric modulated arc therapy (VMAT) is a widely employed radiation therapy technique, showing comparable dosimetry to static beam intensity modulated radiation therapy (IMRT) with reduced monitor units and treatment time. However, the current VMAT optimization has various greedy heuristics employed for an empirical solution, which jeopardizes plan consistency and quality. The authors introduce a novel direct aperture optimization method for VMAT to overcome these limitations.Methods: The comprehensive VMAT (comVMAT) planning was formulated as an optimization problem with an L2-norm fidelity term to penalize the difference between the optimized dose and the prescribed dose, as well as an anisotropic total variation term to promote piecewise continuity in the fluence maps, preparing it for direct aperture optimization. A level set function was used to describe the aperture shapes and the difference between aperture shapes at adjacent angles was penalized to control MLC motion range. A proximal-class optimization solver was adopted to solve the large scale optimization problem, and an alternating optimization strategy was implemented to solve the fluence intensity and aperture shapes simultaneously. Single arc comVMAT plans, utilizing 180 beams with 2. angular resolution, were generated for a glioblastoma multiforme case, a lung (LNG) case, and two head and neck cases-one with three PTVs (H&N-3PTV) and one with foue PTVs (H& N4PTV)-to test the efficacy. The plans were optimized using an alternating optimization strategy. The plans were compared against the clinical VMAT (clnVMAT) plans utilizing two overlapping coplanar arcs for treatment.Results: The optimization of the comVMAT plans had converged within 600 iterations of the block minimization algorithm. comVMAT plans were able to consistently reduce the dose to all organs-at-risk (OARs) as compared to the clnVMAT plans. On average, comVMAT plans reduced the max and mean OAR dose by 6.59% and 7.45%, respectively, of the prescription dose. Reductions in max dose and mean dose were as high as 14.5 Gy in the LNG case and 15.3 Gy in the H&N-3PTV case. PTV coverages measured by D95, D98, and D99 were within 0.25% of the prescription dose. By comprehensively optimizing all beams, the comVMAT optimizer gained the freedom to allow some selected beams to deliver higher intensities, yielding a dose distribution that resembles a static beam IMRT plan with beam orientation optimization.Conclusions: The novel nongreedy VMAT approach simultaneously optimizes all beams in an arc and then directly generates deliverable apertures. The single arc VMAT approach thus fully utilizes the digital Linac's capability in dose rate and gantry rotation speed modulation. In practice, the new single VMAT algorithm generates plans superior to existing VMAT algorithms utilizing two arcs. (C) 2016 American Association of Physicists in Medicine.