Nakazawa Hisato, Uchiyama Yukio, Komori Masataka
Nagoya Radiosurgery Center, Nagoya Kyoritsu Hospital.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2015 Feb;71(2):92-8. doi: 10.6009/jjrt.2015_JSRT_71.2.92.
The objective of this study was to evaluate the reproducibility of dose distributions in stereotactic treatment planning throughout Gamma Knife (GK) stereotactic radiosurgery (SRS) procedures in both GK model C and Perfexion (PFX). An originally-developed phantom and a radiochromic film were used for obtaining actual dose distributions. The phantom, with inserted films, was placed on a Leksell skull frame. Computed tomography (CT) was then acquired with a stereotactic localizer box attached to the frame, dose planning was made using the Leksell GammaPlan treatment planning system, and the phantom was ended up as beam delivery on an equal with clinical radiosurgery process. The reproducibility of the dose plan was provided by distance to agreement (DTA) values between planned and irradiated dose distributions calculated by dedicated film analysis software. The DTA values were determined for the isodose lines at 30%, 50%, 70%, and 90% of the maximum dose. In our study, the reproducibility of dose distributions in GK PFX was lower than in GK model C. As the results common to both units, the mean values of middle dose area (50% isodose) were about half the values of high (90% isodose) and low (30% isodose) dose area. Therefore validation of dose distributions is absolutely essential in commissioning of GK PFX. In addition, when risk organs are close to the target, dose prescription should be normalized for middle isodose line.
本研究的目的是评估在伽玛刀（GK）立体定向放射外科手术（SRS）过程中，GK C型和Perfexion（PFX）型设备立体定向治疗计划中剂量分布的可重复性。使用一种最初开发的模体和一张放射变色胶片来获取实际剂量分布。将插入胶片的模体放置在Leksell头架上。然后使用连接到框架的立体定向定位盒进行计算机断层扫描（CT），使用Leksell GammaPlan治疗计划系统进行剂量规划，并且模体最终如同临床放射外科手术过程一样进行束流照射。剂量计划的可重复性由专用胶片分析软件计算的计划剂量分布与照射剂量分布之间的剂量一致性距离（DTA）值提供。在最大剂量的30%、50%、70%和90%的等剂量线上确定DTA值。在我们的研究中，GK PFX中剂量分布的可重复性低于GK C型。作为两个设备共有的结果，中等剂量区域（50%等剂量）的平均值约为高剂量（90%等剂量）和低剂量（30%等剂量）区域平均值的一半。因此，在GK PFX的调试中，剂量分布的验证绝对必要。此外，当危险器官靠近靶区时，剂量处方应针对中等等剂量线进行归一化。
