Dose domain regularization of MLC leaf patterns for highly complex IMRT plans
Dose domain regularization of MLC leaf patterns for highly complex IMRT plans
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DOI：
10.1118/1.4915286
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发表时间：
2015-04-01
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：
Dan Nguyen;O'Connor, Daniel;Sheng, Ke
目的：自动化光束定向和通量优化的出现使得更复杂的强度调制放射治疗（IMRT）计划使用越来越多的领域来开发扩展的解决方案空间。这在将复杂影响转换为鲁棒多叶准直器（MLC）段以供交付方面带来了挑战。提出了一种正则化影响图和简化MLC片段的新方法，以最大限度地提高交付效率、准确性和计划质量。方法：在这项工作中，我们实现了一种新的方法来正则化优化的剂量域影响。治疗计划问题是在一个优化框架中制定的，以最小化分段引起的剂量分布退化，服从总变差正则化，以鼓励影响图的分段平滑。该优化问题采用一阶原对偶算法Chambolle-Pock算法求解。使用20个自动选择和优化的非共面光束创建2个GBM、2个头颈部和2个肺部患者的计划。首先使用Chambolle-Pock对影响进行正则化，然后将其分层为相等的步骤，并使用先前描述的水平降低方法计算MLC段。从MLC片段中移除尺寸小于预设阈值1-3像素的孤立孔径，这些阈值是来自MLC离散化的IMRT影响图的正方形单位。将剂量域正则化（DDR）影响的性能与不使用剂量域正则化的水平降低的影响的直接分层和直接MLC分割（DMS）进行了比较。结果：DDR方法使6例患者的平均计划靶体积剂量均匀性（D95/D5）从0.814提高到0.878，同时维持危及器官（OARs）的等效剂量。对MLC测序的正则化影响更强，特别是对分层和小孔径去除的影响。对于所有测试的段数，使用DDR的最大和平均孔径尺寸始终大于使用DMS的孔径尺寸。结论：在剂量域中，将通量图与MLC分割转换问题作为二次优化问题，以最小化平滑正则化剂量差异。使用原始对偶算法解决了大规模优化问题，该算法将复杂的影响转化为对MLC分割和测序更具鲁棒性的图，提供更少和更大的片段，并且对剂量分布的降解最小。(C) 2015年美国医学物理学家协会。
Purpose: The advent of automated beam orientation and fluence optimization enables more complex intensity modulated radiation therapy (IMRT) planning using an increasing number of fields to exploit the expanded solution space. This has created a challenge in converting complex fluences to robust multileaf collimator (MLC) segments for delivery. A novel method to regularize the fluence map and simplify MLC segments is introduced to maximize delivery efficiency, accuracy, and plan quality.Methods: In this work, we implemented a novel approach to regularize optimized fluences in the dose domain. The treatment planning problem was formulated in an optimization framework to minimize the segmentation-induced dose distribution degradation subject to a total variation regularization to encourage piecewise smoothness in fluence maps. The optimization problem was solved using a first-order primal-dual algorithm known as the Chambolle-Pock algorithm. Plans for 2 GBM, 2 head and neck, and 2 lung patients were created using 20 automatically selected and optimized noncoplanar beams. The fluence was first regularized using Chambolle-Pock and then stratified into equal steps, and the MLC segments were calculated using a previously described level reducing method. Isolated apertures with sizes smaller than preset thresholds of 1-3 bixels, which are square units of an IMRT fluence map from MLC discretization, were removed from the MLC segments. Performance of the dose domain regularized (DDR) fluences was compared to direct stratification and direct MLC segmentation (DMS) of the fluences using level reduction without dose domain fluence regularization.Results: For all six cases, the DDR method increased the average planning target volume dose homogeneity (D95/D5) from 0.814 to 0.878 while maintaining equivalent dose to organs at risk (OARs). Regularized fluences were more robust to MLC sequencing, particularly to the stratification and small aperture removal. The maximum and mean aperture sizes using the DDR were consistently larger than those from DMS for all tested number of segments.Conclusions: The fluence map to MLC segmentation conversion problem was formulated as a secondary optimization problem in the dose domain to minimize the smoothness-regularized dose discrepancy. The large scale optimization problem was solved using a primal-dual algorithm that transformed complicated fluences into maps that were more robust to the MLC segmentation and sequencing, affording fewer and larger segments with minimal degradation to dose distribution. (C) 2015 American Association of Physicists in Medicine.