Conventional two dimensional and low-definition measurement techniques for dosimetric verification of radiotherapy treatment deliveries are no longer adequate in the era of hypofractionation and extremely high dose gradients. New quality assurance (QA) tools with 3D capability and high definition are urgently needed. The purpose of this study was to evaluate the performance of one of the first such commercial systems as applied to CyberKnife (CK) radiotherapy/radiosurgery system.

This study employed the recently developed commercial 3D patient-specific quality assurance (PSQA) system. Tissue-equivalent radiochromic polymer gel dosimeters, sealed in light protective thin-wall glass spheres (CrystalBalls), were mounted in a high-precision acrylic QA stand. Patient treatment plans were superimposed on the simulator CT scan of one selected CrystalBall and were irradiated in CK machine. CrystalBalls were then scanned using a laser CT scanner (OCTOPUS, MGS Research, Inc., DBA 3D Dosimetry, Madison, CT, USA). The simulator CT scan and the laser CT scan of the CrystalBall were registered in 6D using the VOLQA (MGS Research, Inc., DBA 3D Dosimetry, Madison, CT, USA) software. Planned and delivered dose distributions were compared by means of 3D gamma passing rates at user-selected acceptance criteria. Cumulative 3D dose-volume histograms and overlays of orthogonal profiles and isodoses both in 2D and in 3D were also generated, along with voxel statistics for dose difference and distance-to-agreement criteria. Twelve stereotactic radiosurgery/stereotactic radiotherapy/stereotactic body radiation therapy patients were selected randomly such that each set of two represented one of the six diagnoses: brain metastasis, trigeminal neuralgia, spine metastasis, prostate cancer, lung cancer and liver cancer. The validation of the 3D system was carried out by comparing the 2D gamma passing rates for all the patients using EBT3 films sandwiched between PMMA slabs and then analyzed with PTW VeriSoft software.

The 3D gamma passing rate averaged over all patients studied was (90.5 ± 6.7) % at acceptance criteria of 2% (local) dose difference and 2 mm distance-to-agreement down to 20% isodose. For 3% (local) dose difference and 3 mm distance-to-agreement (also down to 20% cutoff dose), the average passing rate was (96.0 ± 3.1) %.

The results of the study presented here form part of the information needed to assess suitability of a system and hence, the results suggest that the new high-definition 3D CrystalBall system can be a useful PSQA tool as a part of quality assurance for CK.

在超分割和极高的剂量梯度时代，用于放射治疗剂量的剂量学验证的常规二维和低清晰度测量技术已不再足够。迫切需要具有3D功能和高清晰度的新型质量保证（QA）工具。这项研究的目的是评估应用于射波刀（CK）放射治疗/放射外科系统的首批此类商业系统之一的性能。

这项研究采用了最近开发的商业3D患者专用质量保证（PSQA）系统。将与组织等效的放射致变色聚合物凝胶剂量计密封在防光的薄壁玻璃球（CrystalBalls）中，安装在高精度的丙烯酸QA支架中。将患者的治疗计划叠加在所选的一个CrystalBall的模拟器CT扫描上，并在CK机中进行辐照。然后使用激光CT扫描仪（OCTOPUS，MGS Research，Inc.，DBA 3D Dosimetry，麦迪逊，CT，美国）扫描CrystalBall。使用VOLQA（MGS Research，Inc.，DBA 3D Dosimetry，Madison，CT，USA）在6D中注册了CrystalBall的模拟器CT扫描和激光CT扫描。在用户选择的接受标准下，通过3D伽玛通过率比较了计划和交付的剂量分布。还生成了累积的3D剂量-体积直方图以及2D和3D正交图和等位基因的叠加图，以及体素统计数据（用于剂量差异和达成共识的标准）。随机选择十二例立体定向放射外科/立体定向放射治疗/立体定向放射治疗患者，使得每组两组代表以下六个诊断之一：脑转移，三叉神经痛，脊柱转移，前列腺癌，肺癌和肝癌。通过使用夹在PMMA平板之间的EBT3膜比较所有患者的2D伽玛通过率，然后使用PTW VeriSoft软件进行分析，对3D系统进行验证。以及针对剂量差异和达成协议的距离的体素统计信息。随机选择十二名立体定向放射外科/立体定向放射治疗/立体定向放射治疗患者，使得每组两组代表以下六个诊断之一：脑转移，三叉神经痛，脊柱转移，前列腺癌，肺癌和肝癌。通过使用夹在PMMA平板之间的EBT3膜比较所有患者的2D伽玛通过率，然后使用PTW VeriSoft软件进行分析，对3D系统进行验证。以及针对剂量差异和达成协议的距离的体素统计信息。随机选择十二名立体定向放射外科/立体定向放射治疗/立体定向放射治疗患者，使得每组两组代表以下六个诊断之一：脑转移，三叉神经痛，脊柱转移，前列腺癌，肺癌和肝癌。通过使用夹在PMMA平板之间的EBT3膜比较所有患者的2D伽玛通过率，然后使用PTW VeriSoft软件进行分析，对3D系统进行验证。脊柱转移，前列腺癌，肺癌和肝癌。通过使用夹在PMMA平板之间的EBT3膜比较所有患者的2D伽玛通过率，然后使用PTW VeriSoft软件进行分析，对3D系统进行验证。脊柱转移，前列腺癌，肺癌和肝癌。通过使用夹在PMMA平板之间的EBT3膜比较所有患者的2D伽玛通过率，然后使用PTW VeriSoft软件进行分析，对3D系统进行验证。

在接受标准为2％（局部）剂量差异和2mm达成协议距离（低至20％等剂量）的接受标准下，所有研究患者的3D伽玛通过率平均为（90.5±6.7）％。对于3％（局部）剂量差异和3毫米的协议距离（也可降低至20％截止剂量），平均通过率为（96.0±3.1）％。

本文介绍的研究结果构成了评估系统适应性所需信息的一部分，因此，结果表明，新的高清3D CrystalBall系统可以作为CK质量保证的一部分，成为有用的PSQA工具。