基于锥形束CT的宫颈癌患者放疗摆位误差分析

摘要

Objective To investigate how to measure radiotherapy positioning errors for cervical cancer by cone-beam computed tomography (CBCT) so as to analyze the reasons for errors.Methods According to the waist circumference (wc), the patients were divided into three groups: normal (wc≤80 cm), overweight (80 cm < wc < 90 cm), and fat (wc≥90 cm). The positions of 32 cervical cancer patients were stabilized by vacuum bags, and then location CT scan was performed. Before radiotherapy, the images from CBCT was compared to images from location CT to obtain the shift data. Shift data were recorded in the x-axis (left-right), the y-axis (superior-inferior) and z-axis (head-foot) directions. Results The positioning errors on x direction of three groups of patients were (0.8±2.5) mm, (1.5±2.0) mm, (0.2±3.8) mm; the set-up errors on y direction were (-1.3±2.1) mm, (-0.5±2.3) mm, (-0.6±3.5) mm;the set-up errors on z direction were (0.2±3.8) mm, (-0.6±3.5) mm, (0.9±5.5) mm.Conclusion In the course of radiotherapy for cervical cancer patients, image-guided radiotherapy (IGRT) should be selected according to patients’ physical circumstances. As for fat ifgures, with much fat in abdomen or breech, IGRT should be adopted.%目的：应用直线加速器机载锥形束CT（CBCT）研究宫颈癌患者的放疗摆位误差，分析误差原因。方法按腰围大小（wc）将32名宫颈癌患者按腰围分为正常组（wc≤80 cm）、超重组（80 cm＜wc＜90 cm）以及肥胖组（wc≥90 cm）。应用真空袋体模对三组患者进行体位固定，随后行CT扫描定位，在治疗前采用机载CBCT扫描获取图像，并与定位CT图像进行三维配准，记录左右、前后、头脚三个方向（x、 y、z）上的位移数据。结果正常组、超重组、肥胖组患者在x方向上的平均摆位误差分别为（0.8±2.5）mm、（1.5±2.0）mm、（0.2±3.8）mm，在y方向上的平均摆位误差分别为（-1.3±2.1）mm、（-0.5±2.3）mm、（-0.6±3.5）mm，在z方向上的平均摆位误差分别为（0.2±3.8）mm、（-0.6±3.5）mm、（0.9±5.5）mm。结论在宫颈癌患者的放疗过程中，应根据患者的实际情况，判断是否应使用图像引导放疗。对于行动不便、体型较胖或者腹臀部脂肪较多的患者，应尽量采用图像引导放疗。