REAL-TIME TUMOR TRACKING RADIOTHERAPY

器官运动和设置误差一直是使用直线加速器进行放射治疗的最大障碍。我们开发了一种实时肿瘤跟踪放疗（RTRT）系统，该系统每0.03秒检测一次移动肿瘤的位置，精度为*1mm，只有肿瘤的位置与计划位置相对应时才对肿瘤进行照射。在准备过程中，将直径为2.0 mm的圆形金标记物插入肿瘤内或肿瘤附近。肿瘤中心的坐标和金色标记都从计算机断层扫描转移到RTRT。直线室提供两套诊断x射线透视检查，用于在放射治疗期间检测体内的金标记物。实时模式识别技术用于自动识别透视图像中金标记物的投影图形。标记的三维位置是每0.03秒从两个透视图像中计算出来的。只有当金色标记物位于计划位置时，线性加速器才同步照射肿瘤。从识别到照射的时间为0.03秒。在40 mm/s的标记速度下，计划辐照斑与实际辐照斑的差异小于1.0 mm。对于10例不同部位的身体肿瘤患者，将标记物插入肿瘤内部或肿瘤附近。每次治疗时间少于15分钟。中位随访6个月，无并发症及局部复发。实时肿瘤跟踪系统可以显著提高当前体外放疗对机体肿瘤的准确性，并通过减少正常组织的辐照体积，增加放疗的潜力。

Organ motion and setup error have been the largest obstacles in external radiotherapy using the linear accelerator (linac). We have developed a real-time tumor tracking radiotherapy (RTRT) system in which the location of a moving tumor can be detected every 0.03 seconds with an accuracy of *1mm, and the tumor is irradiated only when its location corresponds to the planned position. In preparation, a round gold marker with a diameter of 2.0 mm is inserted in or near the tumor. The coordinates of the tumor center and the gold marker are all transferred from computed tomography to the RTRT.Two sets of diagnostic x-ray fluoroscopy are available in the linac room for detection of the gold marker in the body during radiotherapy. Real-time pattern recognition technology is used for automatic recognition of the projected figure of the gold marker in the fluoroscopic images. The three-dimensional position of the marker is calculated from the two fluoroscopic images every 0.03 seconds. A linear accelerator is synchronized to irradiate the tumor only when the gold marker is located in the planned position. The period between recognition and irradiation is 0.03 seconds. The discrepancy between planned and actual irradiation spot is less than 1.0 mm up to the marker speed of 40 mm/sec. For 10 patients with body tumors in various locations, the marker was inserted into or near the tumor. Treatment time was less than 15 minutes for one session. No complications or local relapses were observed with a median follow-up of 6 months. The real-time tumor tracking system can improve the accuracy of current external radiotherapy for body tumors dramatically, and increase : the potential of radiotherapy by reducing the volume of normal tissue irradiated.