应用OBI系统分析胸部肿瘤调强放疗的摆位误差

目的：应用机载影像系统（on boardinmger，OBl）分析胸部肿瘤调强放射治疗时分次间的摆位误差，并依此计算CTV外扩PTV边界的大小。方法：应用Varian-21EX医用直线加速器治疗47例胸部肿瘤。每周治疗前获取锥形束断层扫描（cone beam computed tomography，CBCT）图像，将CBCT图像和计划CT图像及其靶中心匹配，计算平移和旋转误差。结果：平移误差左右（x）方向为（-0．3194±3．6943）mm，头脚（y）方向为（0．4851±6．2636）mm，前后（z）方向为（0．4144±5．2818）mm；旋转误差冠状面（c）为（0．2080±1．4925）°，矢状面（s）为（0．0922±1．2976）°结沦：对于胸部肿瘤调强放疗（IMRT），临床靶体积（CTV）到计划靶体积（PTV）的外放边界在左右方向宜为7mm，头脚方向宦为11mm，前后方向宜为10mm。考虑到旋转误差，与靶区比较长时靶区两端外放要更大一些.

An analysis of setup error with on board imager for chest tumors treated with intensity modulated radiation therapy

Objective：To analyze the setup errors by on board imager in chest tumor treated with Intensity Modulated Radiotherapy for calculating safety margins of FTV refer to CTV. Metheds：47 patients with chest tumor were treated with Varian - 21EX Linear accelerator. All patients had received cone beam computed tomography（CBCT）before radiotherapy was delivered once a week.The acquired images of cone heron computed tomography were co - registered with planning CT and errors of isocentcr positions on x,y,z axes and rotational deviations were obtained and analyzed. Results：The translational deviations were（ - 0.3194 ± 3.6943）mm, （0.4851 ± 6.2636）mm and（0.4144 ± 5.2818）mm in medi - lateral, cranio - caudal and anterior - posteriar directions, respectively. The rotational deviations were（0.2080± 1.4925）°and（0.0922 ±1.2976）°in sagittal plane and coronal plane, respectively. Conclusions： For the patients with chest tumors undergoing intensity modulated radiation therapy, the margins between the CTV and PTV should be 7 mm in lateral direction, 11 mm in cranio- caudal direction and 10 mm in anterior - posterior direction. Considering thc rotational variations, the margin should be expanded at the end of the target.