通过计划优化后对多叶准直器叶片位置进行细化来提高调强放疗计划质量。

Improving IMRT-plan quality with MLC leaf position refinement post plan optimization.

作者信息

Niu Ying, Zhang Guowei, Berman Barry L, Parke William C, Yi Byongyong, Yu Cedric X

机构信息

Department of Physics, The George Washington University, Washington, DC 20052 , USA.

出版信息

Med Phys. 2012 Aug;39(8):5118-26. doi: 10.1118/1.4737518.

DOI:10.1118/1.4737518

PMID:22894437

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC3416882/

Abstract

PURPOSE

In intensity-modulated radiation therapy (IMRT) planning, reducing the pencil-beam size may lead to a significant improvement in dose conformity, but also increase the time needed for the dose calculation and plan optimization. The authors develop and evaluate a postoptimization refinement (POpR) method, which makes fine adjustments to the multileaf collimator (MLC) leaf positions after plan optimization, enhancing the spatial precision and improving the plan quality without a significant impact on the computational burden.

METHODS

The authors' POpR method is implemented using a commercial treatment planning system based on direct aperture optimization. After an IMRT plan is optimized using pencil beams with regular pencil-beam step size, a greedy search is conducted by looping through all of the involved MLC leaves to see if moving the MLC leaf in or out by half of a pencil-beam step size will improve the objective function value. The half-sized pencil beams, which are used for updating dose distribution in the greedy search, are derived from the existing full-sized pencil beams without need for further pencil-beam dose calculations. A benchmark phantom case and a head-and-neck (HN) case are studied for testing the authors' POpR method.

RESULTS

Using a benchmark phantom and a HN case, the authors have verified that their POpR method can be an efficient technique in the IMRT planning process. Effectiveness of POpR is confirmed by noting significant improvements in objective function values. Dosimetric benefits of POpR are comparable to those of using a finer pencil-beam size from the optimization start, but with far less computation and time.

CONCLUSIONS

The POpR is a feasible and practical method to significantly improve IMRT-plan quality without compromising the planning efficiency.

摘要

目的

在调强放射治疗（IMRT）计划中，减小笔形束尺寸可能会显著改善剂量适形度，但也会增加剂量计算和计划优化所需的时间。作者开发并评估了一种优化后细化（POpR）方法，该方法在计划优化后对多叶准直器（MLC）叶片位置进行微调，提高空间精度并改善计划质量，同时对计算负担没有显著影响。

方法

作者的POpR方法是使用基于直接孔径优化的商业治疗计划系统实现的。在使用具有常规笔形束步长的笔形束对IMRT计划进行优化后，通过遍历所有涉及的MLC叶片进行贪婪搜索，以查看将MLC叶片移入或移出半个笔形束步长是否会改善目标函数值。用于在贪婪搜索中更新剂量分布的半尺寸笔形束是从现有的全尺寸笔形束导出的，无需进一步的笔形束剂量计算。研究了一个基准体模病例和一个头颈部（HN）病例来测试作者的POpR方法。