Bogner Joachim, Petersch Bernhard, Georg Dietmar, Dieckmann Karin, Zehetmayer Martin, Pötter Richard
Department of Radiotherapy and Radiobiology, University of Vienna, Vienna, Austria.
Int J Radiat Oncol Biol Phys. 2003 Jul 15;56(4):1128-36. doi: 10.1016/s0360-3016(03)00280-3.
To introduce a noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy for uveal melanoma.
At the Department of Radiotherapy and Radiobiology, University of Vienna, stereotactic radiotherapy is offered to patients with uveal melanoma considered unsuitable for (106)Ru brachytherapy or local resection. For the present feasibility study, 8 patients were carefully selected according to their ability to fixate a small light source with the diseased eye and whether they had a rather small head to meet the limited geometric space available. A polymethyl methacrylate tube was attached to a stereotactic mask system in craniocaudal orientation supporting a 45 degrees mirror, which was placed in front of the diseased eye. At the other end of the tube, the patient was given a small fixation light, and a small camera was positioned beneath, which was shielded for use during MRI. A computer interface calculated and visualized the spatial difference of the actual and a given reference pupil position, which was defined before CT scanning, during the MRI sequences, and during treatment delivery at the linear accelerator.
The described system can be attached to a conventional stereotactic mask system with minor modifications. Because of the large distance between the eye and the fixation light, the optical fixation system was well tolerated by all patients, and a stable position of the eye was obtained. The camera system can be used during CT and MRI without interference. Absorption of the 6-MV photon beam by the mirror and the polymethyl methacrylate tube was negligible. The computer interface designed to determine the pupil position uses an image-processing algorithm that correlates a template of the reference image with the actual image of the eye. Provided sufficient illumination of the pupil, the correlation function showed a pronounced minimum at the reference position. The precision of the algorithm was tested by phantom measurements. For a given 1 mm or 2 mm displacement, the interface reported a mean shift of 0.96 +/- 0.18 mm or 2.07 +/- 0.11 mm, respectively.
The results of this study demonstrated the feasibility of a new optical fixation system for linear accelerator-based stereotaxis. The artifact-free application of the camera system during image acquisition and irradiation and the use of the computer interface, which automatically monitored eye movements with submillimeter precision, provided large improvements compared with existing techniques. Given well-defined interruption criteria and accelerated image processing, the described system has a high potential to perform automatically gated treatment beam delivery in the near future.
介绍一种用于基于直线加速器的葡萄膜黑色素瘤立体定向放射治疗的非侵入性眼固定和计算机辅助眼监测系统。
在维也纳大学放射治疗与放射生物学系，为被认为不适合（106）Ru近距离放疗或局部切除的葡萄膜黑色素瘤患者提供立体定向放射治疗。在本可行性研究中，根据患者用患眼固定小光源的能力以及他们的头部是否较小以适应有限的可用几何空间，精心挑选了8名患者。一根聚甲基丙烯酸甲酯管以头足方向连接到立体定向面罩系统上，支撑着一面45度的镜子，该镜子放置在患眼前方。在管子的另一端，给患者一个小的固定光源，在其下方放置一个小摄像头，该摄像头在MRI期间使用时进行了屏蔽。一个计算机接口计算并可视化实际瞳孔位置与给定参考瞳孔位置的空间差异，该参考瞳孔位置在CT扫描前、MRI序列期间以及直线加速器治疗期间定义。
所描述的系统可以通过微小修改连接到传统的立体定向面罩系统上。由于眼睛与固定光源之间的距离较大，所有患者对光学固定系统的耐受性良好，并且获得了眼睛的稳定位置。摄像头系统可在CT和MRI期间使用而不会产生干扰。镜子和聚甲基丙烯酸甲酯管对6-MV光子束的吸收可忽略不计。设计用于确定瞳孔位置计算机接口使用一种图像处理算法，该算法将参考图像的模板与眼睛的实际图像相关联。在瞳孔有足够照明的情况下，相关函数在参考位置显示出明显的最小值。该算法的精度通过体模测量进行了测试。对于给定的1毫米或2毫米位移，该接口分别报告平均偏移为0.96±0.18毫米或2.07±0.11毫米。
本研究结果证明了一种用于基于直线加速器立体定向的新型光学固定系统的可行性。与现有技术相比，摄像头系统在图像采集和照射期间无伪影的应用以及使用能以亚毫米精度自动监测眼球运动的计算机接口有了很大改进。给定明确的中断标准和加速的图像处理，所描述的系统在不久的将来有很大潜力执行自动门控治疗束输送。
