腹盆部肿瘤在放疗分次内的摆位误差分析

[目的]应用医科达Synergy系统的锥形束CT（cone beam computed tomography,CBCT）研究腹盆部肿瘤患者在放疗分次内的摆位误差变化情况。[方法]对17例腹盆部肿瘤患者进行治疗,每次照射前进行首次摆位的CBCT扫描,然后与计划CT图象进行匹配,获得平移方向（x、y、z）和旋转方向（u、v、w）的摆位误差,通过完全由计算机控制的全碳素纤维六足遥控床进行自动的摆位误差纠正,误差调整后再次获取CBCT图像,分析并记录误差纠正后的残留误差。当患者治疗结束后,第三次获取CBCT图象,分析治疗后的体位误差,并与治疗前误差纠正后的残留误差相比较,从而得出患者在治疗过程中的分次内摆位误差情况。[结果]17例患者进行CBCT扫描672次,每次治疗开始前首次摆位、误差纠正后和治疗结束后的CBCT扫描均为224次。治疗前误差纠正后的系统误差（均数）±随机误差（标准差）在x、y、z、u、v、w六自由度方向上分别为（0.01±0.36）mm、（-0.40±0.65）mm、（-0.01±0.63）mm、（0.1±0.5）°、（0.1±0.5）°、（0.0±0.4）°,患者治疗结束后测量的误差分别为（-0.01±0.51）mm、（-0.77±0.84）mm、（-0.10±0.70）mm、（0.1±0.6）°、（0.1±0.5）°、（0.0±0.4）°;配对t检验y、z方向差异显著,P值分别为：0.000、0.041。[结论]腹盆部肿瘤在治疗过程中存在一定的分次内摆位误差,这在临床上设计PTV的摆位扩边应予以考虑。

Analysis of the Intrafractional Setup Errors in Radiotherapy for Abdominal-pelvic Tumors

[Purpose] To analyze the intrafractional setup errors in radiotherapy for abdominal-pelvic tumors using cone-beam computed tomography （CBCT） of Elekta. [Methods] 17 patients with abdominal-pelvic tumor received radiotherapy. They received CBCT scans after initial setup , then the CBCT images were registered to the planning CT images, and setup errors on translational directions（x, y, z） and on rotational directions（u, v, w） were obtained and analyzed .After corrected by the Hexapod Robot Treatment Table controlled by computer, the second CBCT was performed and the residual errors of the post-correction were recorded. After radiation delivery, patients received the third CBCT, and the setup errors were analyzed and compared with that of post-correction. [Results] A total of 672 CBCT scans were performed on 17 patients, with 224 scans performed, both before and after correction and after radiation delivery. The residual errors after correction on x, y, z, u, v and w directions were（0.01±0.36）mm, （-0.40±0.65）mm, （-0.01±0.63）mm, （0.1±0.5）°, （0.1±0.5）°, （0.0±0.4）° respectively, and the errors after treatment were （-0.01±0.51）mm, （-0.77±0.84）mm, （-0.10±0.70）mm, （0.1±0.6）°, （0.1±0.5）°and （0.0±0.4）°respectively. The Paired Samples Test indicated that there were significantly differences on the y axis （P=0.000） and z axis（P=0.041）. [Conclusions] The intrafractional setup error variations exist in radiotherapy for abdominal-pelvic tumors and should be taken into account during deciding the clinical margin of PTV.