锥形束CT在肺癌患者精确放疗摆位误差研究

目的利用锥形束CT引导分析16例肺癌患者精确放疗分次治疗间的误差,探讨临床靶区外放边界.方法选取采用图像引导放疗(image-guided radiation therapy,IGRT)的16例肺癌患者,其中左肺癌9例,右肺癌5例,肺癌纵隔淋巴结转移2例.所有患者均采用热塑体模固定,每天行IGRT,根据锥形束CT图像与计划CT图像相匹配,选取每例患者扫描数据,研究其相对于计划CT左右(x)、头脚(y)、垂直(z)的摆位误差.结果 x、y、z轴的线性摆位误差(系统误差±随机误差)分别为(0.11±0.06)cm、(0.14±0.10)cm、(-0.04±0.06)cm,其旋转轴上的误差分别为0.57°±0.17°、0.05°±0.20°、-0.01°±0.33°.相对来说y方向的摆位误差较x、z方向大.结论锥形束CT的应用明显减少了肺癌患者放疗摆位误差,同时为减少摆位误差影响CTV外放PTV时,考虑x方向外扩0.62cm、y方向0.82cm、z方向0.49cm.

Set-up errors of cone-beam CT in precision radiotherapy for patients with lung cancer

Objective To study the set-up margin of clinical target area by analyzing the set-up errors of cone-beam CT in 16 lung cancer patients undergoing fractioned radiotherapy.Methods Sixteen patients with lung cancer(8 with left lung cancer,5 with right lung cancer and 2 with mediastinal lymphanode metastasis) who underwent image-guided radiation therapy(IGRT)were included in this study.All patients were fixed with thermoplast phantom and underwent IGRT every day.Set-up errors of cone-beam CT were calculated according to its matched and planned CT images in left-right(x),superior-inferior(y) and anterior-posterior(z) directions.Results The set-up error of cone-beam CT in the x,y and z axes was(0.11±0.06)cm,(0.14±0.10)cm and(-0.04±0.06)cm respectively,while the set-up error of cone-beam CT in its rotary axis was 0.57°±0.17°,0.05°±0.20°and-0.01°±0.33°,respectively.The set-up error of cone-beam CT in the y direction was relatively larger than in the x and z direction.Conclusion Application of one-beam CT can significantly reduce the set-up errors of radiotherapy in patients with lung cancer and the effect on PTV margin with an outward extension of 0.62cm,0.82cm and 0.49cm in the x,y and z directions,respectively.