Independent calculation of monitor units for VMAT and SPORT
Independent calculation of monitor units for VMAT and SPORT
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DOI：
10.1118/1.4906185
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发表时间：
2015-02-01
期刊：
影响因子：
3.8
通讯作者：
Xing, Lei
中科院分区：
文献类型：
--
作者：
Chen, Xin;Bush, Karl;Xing, Lei
目的：剂量和监测单位（MU）代表了放射治疗的两个重要方面。在当前实践中，治疗计划的验证通常在剂量域中完成，其中执行体模测量或前向剂量计算以检查给定治疗计划的剂量测定准确度和MU设置。虽然希望直接验证MU设置，但尚未开发用于从已知剂量分布获得MU值的计算框架。本文提出了一种从给定的剂量分布中独立计算体积调制式弧形放射治疗（VMAT）和站参数优化放射治疗（SPORT）的MU的策略。方法：一个点的剂量可以表示为所有站点（或控制点）的贡献之和。这种关系形成了建议MU验证技术的基础。为了继续进行，作者首先通过计算一系列体素处的剂量（通常在VMAT/SPORT治疗计划的处方表面上）获得表征所涉及的站点的剂量测定贡献的矩阵元素，其中所有站点的单位MU设置。使用内部Monte Carlo（MC）软件进行剂量矩阵计算。然后，通过最小化由治疗计划系统（TPS）计算的剂量与针对处方表面上的所选体素集合的MC的剂量之间的最小二乘差来导出站点的MU。该技术应用于16例临床病例的各种能量，疾病部位，和TPS剂量计算algorithm.Results：对于所有计划，除了肺组织密度不均匀性大的情况下，独立计算的MU与TPS的所有站点一致，在2.7%。在剂量域中，MC和Eclipse各向异性分析算法（AAA）剂量分布之间在这些病例的等剂量轮廓、剂量曲线、伽马指数和剂量体积直方图（DVH）方面无显著差异。对于肺部病例，MC计算的MU与使用AAA计算的治疗计划的MU显著不同。然而，当TPS剂量计算算法切换到基于传输方程的技术（Acuros T）时，差异减少到3%以内。MC和Eclipse AAA/Acuros计算之间的剂量域的比较得出的结论与MU calculation.Conclusions一致：已经建立了一个与MU和剂量域相关的计算框架。该框架不仅使他们能够直接在MU域中验证VMAT计划的所涉及站点的MU值，而且还提供了一种非常需要的机制，以根据剂量域中的特定变化自适应地修改站点的MU值。(C)2015年作者。
Purpose: Dose and monitor units (MUs) represent two important facets of a radiation therapy treatment. In current practice, verification of a treatment plan is commonly done in dose domain, in which a phantom measurement or forward dose calculation is performed to examine the dosimetric accuracy and the MU settings of a given treatment plan. While it is desirable to verify directly the MU settings, a computational framework for obtaining the MU values from a known dose distribution has yet to be developed. This work presents a strategy to calculate independently the MUs from a given dose distribution of volumetric modulated arc therapy (VMAT) and station parameter optimized radiation therapy (SPORT).Methods: The dose at a point can be expressed as a sum of contributions from all the station points (or control points). This relationship forms the basis of the proposed MU verification technique. To proceed, the authors first obtain the matrix elements which characterize the dosimetric contribution of the involved station points by computing the doses at a series of voxels, typically on the prescription surface of the VMAT/SPORT treatment plan, with unit MU setting for all the station points. An in-house Monte Carlo (MC) software is used for the dose matrix calculation. The MUs of the station points are then derived by minimizing the least-squares difference between doses computed by the treatment planning system (TPS) and that of the MC for the selected set of voxels on the prescription surface. The technique is applied to 16 clinical cases with a variety of energies, disease sites, and TPS dose calculation algorithms.Results: For all plans except the lung cases with large tissue density inhomogeneity, the independently computed MUs agree with that of TPS to within 2.7% for all the station points. In the dose domain, no significant difference between the MC and Eclipse Anisotropic Analytical Algorithm (AAA) dose distribution is found in terms of isodose contours, dose profiles, gamma index, and dose volume histogram (DVH) for these cases. For the lung cases, the MC-calculated MUs differ significantly from that of the treatment plan computed using AAA. However, the discrepancies are reduced to within 3% when the TPS dose calculation algorithm is switched to a transport equation-based technique (Acuros T). Comparison in the dose domain between the MC and Eclipse AAA/Acuros calculation yields conclusion consistent with the MU calculation.Conclusions: A computational framework relating the MU and dose domains has been established. The framework does not only enable them to verify the MU values of the involved station points of a VMAT plan directly in the MU domain but also provide a much needed mechanism to adaptively modify the MU values of the station points in accordance to a specific change in the dose domain. (C) 2015 Author(s).