Treuer H, Hunsche S, Hoevels M, Luyken K, Maarouf M, Voges J, Sturm V
Department of Stereotaxy and Functional Neurosurgery, University of Cologne, 50924 Cologne, Germany.
Phys Med Biol. 2004 Sep 7;49(17):3877-87. doi: 10.1088/0031-9155/49/17/004.
A strong attachment of a stereotactic head frame to the patient's skull may cause distortions of the head frame. The aim of this work was to identify possible distortions of the head frame, to measure the degree of distortion occurring in clinical practice and to investigate its influence on stereotactic localization and targeting. A model to describe and quantify the distortion of the Riechert-Mundinger (RM) head frame was developed. Distortions were classified as (a) bending and (b) changes from the circular ring shape. Ring shape changes were derived from stereotactic CT scans and frame bending was determined from intraoperative stereotactic x-ray images of patients with implanted 125I-seeds acting as landmarks. From the examined patient data frame bending was determined to be 0.74 mm+/-0.32 mm and 1.30 mm in maximum. If a CT-localizer with a top ring is used, frame bending has no influence on stereotactic CT-localization. In stereotactic x-ray localization, frame bending leads to an overestimation of the z-coordinate by 0.37 mm+/-0.16 mm on average and by 0.65 mm in maximum. The accuracy of patient positioning in radiosurgery is not affected by frame bending. But in stereotactic surgery with an RM aiming bow trajectory displacements are expected. These displacements were estimated to be 0.36 mm+/-0.16 mm (max. 0.74 mm) at the target point and 0.65 mm+/-0.30 mm (max. 1.31 mm) at the entry point level. Changes from the circularring shape are small and do not compromise the accuracy of stereotactic targeting and localization. The accuracy of CT-localization was found to be close to the resolution limit due to voxel size. Our findings for frame bending of the RM frame could be validated by statistical analysis and by comparison with an independent patient examination. The results depend on the stereotactic system and details of the localizers and instruments and also reflect our clinical practice. Therefore, a generalization is not possible. Preliminary experience with a new MR-compatible RM head frame made of ceramics shows no frame distortions as with the conventional frame made of an Al-Cu-Mg alloy.
立体定向头架与患者颅骨的牢固连接可能会导致头架变形。本研究的目的是识别头架可能出现的变形，测量临床实践中发生的变形程度，并研究其对立体定向定位和靶点确定的影响。开发了一个用于描述和量化里歇特 - 蒙丁格（RM）头架变形的模型。变形分为（a）弯曲和（b）偏离圆环形状。圆环形状的变化通过立体定向CT扫描得出，框架弯曲则根据植入125I种子作为标志物的患者术中立体定向X线图像确定。根据检查的患者数据，确定框架弯曲为0.74 mm±0.32 mm，最大为1.30 mm。如果使用带有顶环的CT定位器，框架弯曲对立体定向CT定位没有影响。在立体定向X线定位中，框架弯曲平均会导致z坐标高估0.37 mm±0.16 mm，最大高估0.65 mm。放射外科中患者定位的准确性不受框架弯曲影响。但在使用RM瞄准弓进行立体定向手术时，预计会出现轨迹位移。这些位移在靶点处估计为0.36 mm±0.16 mm（最大0.74 mm），在入口点水平为0.65 mm±0.30 mm（最大1.31 mm）。偏离圆环形状的变化很小，不会影响立体定向靶点确定和定位的准确性。由于体素大小，发现CT定位的准确性接近分辨率极限。我们关于RM框架弯曲的研究结果可以通过统计分析以及与独立患者检查结果进行比较来验证。结果取决于立体定向系统、定位器和器械的细节，也反映了我们的临床实践。因此，无法进行推广。使用由陶瓷制成新型磁共振兼容RM头架的初步经验表明，与由铝 - 铜 - 镁合金制成的传统框架不同，该头架没有框架变形。
