针对专用多源颅内放射外科治疗单元，考虑重叠结构和剂量均匀性，实现自动化治疗计划。

Automated treatment planning for a dedicated multi-source intra-cranial radiosurgery treatment unit accounting for overlapping structures and dose homogeneity.

机构信息

Department of Mechanical and Industrial Engineering, University of Toronto, Ontario M5S 3G8, Canada.

出版信息

Med Phys. 2013 Sep;40(9):091715. doi: 10.1118/1.4817555.

DOI:10.1118/1.4817555

PMID:24007148

Abstract

PURPOSE

The purpose of this work is to advance the two-step approach for Gamma Knife(®) Perfexion™ (PFX) optimization to account for dose homogeneity and overlap between the planning target volume (PTV) and organs-at-risk (OARs).

METHODS

In the first step, a geometry-based algorithm is used to quickly select isocentre locations while explicitly accounting for PTV-OARs overlaps. In this approach, the PTV is divided into subvolumes based on the PTV-OARs overlaps and the distance of voxels to the overlaps. Only a few isocentres are selected in the overlap volume, and a higher number of isocentres are carefully selected among voxels that are immediately close to the overlap volume. In the second step, a convex optimization is solved to find the optimal combination of collimator sizes and their radiation duration for each isocentre location.

RESULTS

This two-step approach is tested on seven clinical cases (comprising 11 targets) for which the authors assess coverage, OARs dose, and homogeneity index and relate these parameters to the overlap fraction for each case. In terms of coverage, the mean V99 for the gross target volume (GTV) was 99.8% while the V95 for the PTV averaged at 94.6%, thus satisfying the clinical objectives of 99% for GTV and 95% for PTV, respectively. The mean relative dose to the brainstem was 87.7% of the prescription dose (with maximum 108%), while on average, 11.3% of the PTV overlapped with the brainstem. The mean beam-on time per fraction per dose was 8.6 min with calibration dose rate of 3.5 Gy/min, and the computational time averaged at 205 min. Compared with previous work involving single-fraction radiosurgery, the resulting plans were more homogeneous with average homogeneity index of 1.18 compared to 1.47.

CONCLUSIONS

PFX treatment plans with homogeneous dose distribution can be achieved by inverse planning using geometric isocentre selection and mathematical modeling and optimization techniques. The quality of the obtained treatment plans are clinically satisfactory while the homogeneity index is improved compared to conventional PFX plans.

摘要

目的

本研究旨在提出一种两步法来优化伽玛刀（®） Perfexion（PFX），以考虑靶区（PTV）与危及器官（OAR）之间的剂量均匀性和重叠问题。

方法

在第一步中，采用基于几何的算法快速选择等中心点位置，同时明确考虑 PTV-OAR 重叠问题。在此方法中，根据 PTV-OAR 重叠和体素到重叠的距离，将 PTV 分为子容积。仅在重叠体积中选择少数几个等中心点，而在紧邻重叠体积的体素中仔细选择更多的等中心点。在第二步中，求解凸优化问题，以找到每个等中心点位置的准直器大小及其辐射持续时间的最佳组合。

结果

本两步法应用于 7 个临床病例（包括 11 个靶区），作者评估了这些病例的覆盖程度、OAR 剂量和均匀性指数，并将这些参数与每个病例的重叠分数相关联。在覆盖程度方面，大体靶区（GTV）的 99.8%的体积达到了 99%，而 PTV 的 95%的体积达到了 94.6%，分别满足 GTV 为 99%和 PTV 为 95%的临床目标。脑干的平均相对剂量为处方剂量的 87.7%（最大为 108%），平均有 11.3%的 PTV 与脑干重叠。每个剂量的每个分数的平均照射时间为 8.6 分钟，校准剂量率为 3.5 Gy/min，计算时间平均为 205 分钟。与以前的单次分割放射外科手术的工作相比，所得计划的均匀性更好，平均均匀性指数为 1.18，而不是 1.47。