Lohr F, Debus J, Frank C, Herfarth K, Pastyr O, Rhein B, Bahner M L, Schlegel W, Wannenmacher M
Department of Clinical Radiology, University of Heidelberg, Germany.
Int J Radiat Oncol Biol Phys. 1999 Sep 1;45(2):521-7. doi: 10.1016/s0360-3016(99)00190-x.
To evaluate the setup accuracy that can be achieved with a novel noninvasive patient fixation technique based on a body cast attached to a recently developed stereotactic body frame during fractionated extracranial stereotactic radiotherapy.
Thirty-one CT studies (> or = 20 slices, thickness: 3 mm) from 5 patients who were immobilized in a body cast attached to a stereotactic body frame for treatment of paramedullary tumors in the thoracic or lumbar spine were evaluated with respect to setup accuracy. The immobilization device consisted of a custom-made wrap-around body cast that extended from the neck to the thighs and a separate head mask, both made from Scotchcast. Each CT study was performed immediately before or after every second or third actual treatment fraction without repositioning the patient between CT and treatment. The stereotactic localization system was mounted and the isocenter as initially located stereotactically was marked with fiducials for each CT study. Deviation of the treated isocenter as compared to the planned position was measured in all three dimensions.
The immobilization device can be easily handled, attached to and removed from the stereotactic frame and thus enables treatment of multiple patients with the same stereotactic frame each day. Mean patient movements of 1.6 mm+/-1.2 mm (laterolateral [LL]), 1.4 mm+/-1.0 mm (anterior-posterior [AP]), 2.3 mm+/-1.3 mm (transversal vectorial error [VE]) and < slice thickness = 3 mm (craniocaudal [CC]) were recorded for the targets in the thoracic spine and 1.4 mm+/-1.0 mm (LL), 1.2 mm+/-0.7 mm (AP), 1.8 mm+/-1.2 mm (VE), and < 3 mm (CC) for the lumbar spine. The worst case deviation was 3.9 mm for the first patient with the target in the thoracic spine (in the LL direction). Combining those numbers (mean transversal VE for both locations and maximum CC error of 3 mm), the mean three-dimensional vectorial patient movement and thus the mean overall accuracy can be safely estimated to be < or = 3.6 mm.
The presented combination of a body cast and head mask system in a rigid stereotactic body frame ensures reliable noninvasive patient fixation for fractionated extracranial stereotactic radiotherapy and may enable dose escalation for less radioresponsive tumors that are near the spinal cord or otherwise critically located while minimizing the risk of late sequelae.
评估一种新型无创患者固定技术的摆位精度，该技术基于在分次颅外立体定向放射治疗期间，将附着于最近开发的立体定向体架上的全身石膏固定装置用于患者固定。
对5例患者的31份CT研究（≥20层，层厚：3mm）进行评估，这些患者被固定在附着于立体定向体架的全身石膏固定装置中，用于治疗胸段或腰段脊柱旁肿瘤的摆位精度。固定装置由一个定制的环绕式全身石膏固定装置组成，该装置从颈部延伸至大腿，以及一个单独的头部面罩，两者均由Scotchcast制成。每次CT研究在每隔一次或第三次实际治疗分次之前或之后立即进行，在CT扫描和治疗之间患者无需重新摆位。安装立体定向定位系统，并在每次CT研究中用基准标记最初立体定向定位的等中心。测量治疗等中心相对于计划位置在所有三个维度上的偏差。
该固定装置易于操作，可附着于立体定向体架并从其上移除，因此能够每天使用同一立体定向体架对多名患者进行治疗。记录到胸段脊柱靶区的平均患者移动为1.6mm±1.2mm（左右方向[LL]）、1.4mm±1.0mm（前后方向[AP]）、2.3mm±1.3mm（横向矢量误差[VE]）和<层厚=3mm（头脚方向[CC]），腰段脊柱靶区的平均患者移动为1.4mm±1.0mm（LL）、1.2mm±0.7mm（AP）、1.8mm±1.2mm（VE）和<3mm（CC）。第一位胸段脊柱有靶区的患者的最坏情况偏差为3.9mm（在LL方向）。综合这些数据（两个部位的平均横向VE以及最大CC误差为3mm），平均三维矢量患者移动以及因此平均总体精度可以安全地估计为≤3.6mm。
在刚性立体定向体架中采用的全身石膏固定装置与头部面罩系统相结合，可确保在分次颅外立体定向放射治疗中实现可靠的无创患者固定，并可能使靠近脊髓或以其他方式处于关键位置的放射反应性较低的肿瘤能够增加剂量，同时将晚期后遗症的风险降至最低。
