Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
Medical Physics and Gamma Knife Department, Hygeia Hospital, Marousi, Greece.
J Appl Clin Med Phys. 2022 May;23(5):e13580. doi: 10.1002/acm2.13580. Epub 2022 Mar 14.
In frame-based Gamma Knife (GK) stereotactic radiosurgery two treatment planning workflows are commonly employed; one based solely on magnetic resonance (MR) images and the other based on magnetic resonance/computed tomography (MR/CT) co-registered images. In both workflows, target localization accuracy (TLA) can be deteriorated due to MR-related geometric distortions and/or MR/CT co-registration uncertainties. In this study, the overall TLA following both clinical workflows is evaluated for cases of multiple brain metastases.
A polymer gel-filled head phantom, having the Leksell stereotactic headframe attached, was CT-imaged and irradiated by a GK Perfexion unit. A total of 26 4-mm shots were delivered at 26 locations directly defined in the Leksell stereotactic space (LSS), inducing adequate contrast in corresponding T2-weighted (T2w) MR images. Prescribed shot coordinates served as reference locations. An additional MR scan was acquired to implement the "mean image" distortion correction technique. The TLA for each workflow was assessed by comparing the radiation-induced target locations, identified in MR images, with corresponding reference locations. Using T1w MR and CT images of 15 patients (totaling 81 lesions), TLA in clinical cases was similarly assessed, considering MR-corrected data as reference. For the MR/CT workflow, both global and region of interest (ROI)-based MR/CT registration approaches were studied.
In phantom measurements, the MR-corrected workflow demonstrated unsurpassed TLA (median offset of 0.2 mm) which deteriorated for MR-only and MR/CT workflows (median offsets of 0.8 and 0.6 mm, respectively). In real-patient cases, the MR-only workflow resulted in offsets that exhibit a significant positive correlation with the distance from the MR isocenter, reaching 1.1 mm (median 0.6 mm). Comparable results were obtained for the MR/CT-global workflow, although a maximum offset of 1.4 mm was detected. TLA was improved with the MR/CT-ROI workflow resulting in median/maximum offsets of 0.4 mm/1.1 mm.
Subpixel TLA is achievable in all workflows. For the MR/CT workflow, a ROI-based MR/CT co-registration approach could considerably increase TLA and should be preferred instead of a global registration.
在基于框架的伽玛刀（GK）立体定向放射外科中，通常采用两种治疗计划工作流程；一种仅基于磁共振（MR）图像，另一种基于磁共振/计算机断层扫描（MR/CT）配准图像。在这两种工作流程中，由于与 MR 相关的几何变形和/或 MR/CT 配准不确定性，靶定位准确性（TLA）可能会降低。在这项研究中，评估了两种临床工作流程后，多发性脑转移病例的整体 TLA。
将带有 Leksell 立体定向头架的聚合物凝胶填充头体模进行 CT 成像，并由 GK Perfexion 单元进行照射。总共在 26 个位置以 26 个位置进行 4 毫米的 26 次射击，直接在 Leksell 立体定向空间（LSS）中定义，在相应的 T2 加权（T2w）MR 图像中诱导出足够的对比度。规定的射击坐标用作参考位置。采集额外的 MR 扫描以实施“平均图像”失真校正技术。通过比较在 MR 图像中识别的辐射诱导的靶位置与相应的参考位置，评估每个工作流程的 TLA。使用 15 名患者的 T1w MR 和 CT 图像（总计 81 个病变），同样考虑 MR 校正数据作为参考，评估临床病例中的 TLA。对于 MR/CT 工作流程，研究了全局和感兴趣区域（ROI）的基于 MR/CT 的注册方法。
在体模测量中，MR 校正工作流程显示出无与伦比的 TLA（中位数偏移量为 0.2 毫米），而仅使用 MR 和 MR/CT 工作流程时则恶化（中位数偏移量分别为 0.8 和 0.6 毫米）。在实际患者病例中，仅使用 MR 的工作流程导致的偏移量与距 MR 等中心的距离呈显著正相关，达到 1.1 毫米（中位数 0.6 毫米）。对于 MR/CT-全局工作流程，获得了类似的结果，尽管检测到最大偏移量为 1.4 毫米。通过使用 MR/CT-ROI 工作流程，可以改善 TLA，从而使中位数/最大偏移量分别达到 0.4 毫米/1.1 毫米。
在所有工作流程中都可以实现亚像素 TLA。对于 MR/CT 工作流程，基于 ROI 的 MR/CT 配准方法可以大大提高 TLA，应该优先选择而不是全局配准。
