锥形束CT图象引导放疗的应用性测试

Application Testing for Cone-beam CT Image-guided Radiation Therapy

目的:探索一种针对锥形束CT图象引导放疗的应用性测试新方法,测试锥形束CT图象引导的准确性。方法:设计一个应用性测度专用模体:用10 cm厚马克力聚苯乙烯板围成一个长方体,模体内在上下、左右和前后三个方向上分别建立三根小梁,每根小梁都贯穿模体,与模体中相对的两个面相连。模体的每个面的中心设有"十"字标识。把模体平放在PHILIPS大孔径CT检查床面上,用CT机房内的激光灯分别对准模体左、右和上面中心,扫描获取用于设计放疗计划的CT图象。该图象经VARIS网络传到Eclipse放疗计划系统,用Eclipse设计计划,射野中心位于模体中心。把模体平放到VARIAN加速器治疗床面上,用加速器机房内的激光灯分别对准模体左、右和上面中心。VARIAN加速器配有OBI(On-Board Imager)系统,用锥形束CT扫描,获得模体的摆位图象,并与计划图象配准。结果:设计放疗计划的参考图象与摆位图象具有相同的特征,在模体的横截面、矢状面和寇状面上都有三个小梁的横截面,截面的边界清晰,图像配准显示在侧向和竖直方向的位置误差均为0.0 cm,在纵向位置误差0.1 cm,旋转误差0.0°。结论:利用本文设计的应用性测试专模体完成应用性测试是一种简便且可靠的方法。

objective： To probe a new application testing for cone-beam CT image-guided radiation therapy and find the geomet- rical uncertainties during radiation therapy using cone beam CT. Methods： The phantom is designed for the application testing for cone-beam CT image-guided radiation therapy.The phantom includes a cuboid shell made of polystyrene.The thickness of the shell is 10 cm.There are 3 polstyrene beams in each direction： up-down,left-right,and ant-post. Each beam is fixed on the two op- posite walls of the shell. There is a ＂＋＂ sign in the center of each wall of the shell. The phantom is placed on the couch of the Brilliance big core CT and the three laser crosses in the CT room align the three ccnter ＂＋＂ signs in the left,right and top wall of the phantom respectively. The reference images of the phantom are acquired using the CT and translated to the Varian Eclipse planning system through VARIS. The isocenter of the treatment fields is on the center of the phantom. The phantom is placed on the couch of the accelerator and the three laser crosses in the accelerator room align the three ccnter ＂＋＂ signs in the left,right and top wall of the phantom respectively. The cone-beam CT provides the setup images of the phantom using the on-board imaging componets mounted on the Varian accelerator. The setup images and the reference images are compared and registered using the vendor software. Results： The reference images and the setup images have the same character： three transversal images of the beams in the phantom transversal image,coronal image, sagittal image. The shifts of the couch movement from the target position to the actual position are shown： the shift is 0.0 cm in the couch Vrt dirction, 0.0 cm in the couch Lat dirction, -0.1 cm in the couch Lng direction, 0.0 degrees in the couch Rtn direction. Conclusions： the application testing using the special phantom for image-guided radiation therapy is easy and reliable,