基于3DCT与CBCT勾画的胸中下段食管癌内在大体肿瘤靶区的比较

Comparison of internal gross target volume in thoracic middle and lower segment esophageal cancer based on 3DCT and CBCT

目的比较基于三维CT(3DCT)和锥形束CT(CBCT)图像定义的胸中下段食管癌内在大体肿瘤靶区即内靶区的体积(IGTV)及匹配度。方法 15例胸中下段食管癌患者,首先完成胸部3DCT扫描,基于3DCT制定放疗计划,在3DCT上勾画得到GTV3D,依据山东省肿瘤医院通过四维CT(4DCT)图像测得的胸中下段食管癌靶区运动范围95%可信区间上限外扩得到IGTV,胸中下段食管癌GTV头脚、前后、左右方向分别外扩6.0、3.0、3.0 mm得到IGTV3D,放疗治疗前5次拍摄CBCT,并基于骨性标志配准校正,在CBCT图像上勾画得到IGTVCBCT。比较IGTV3D与IGTVCBCT靶区间体积及匹配度。结果 IGTV3D大于IGTVCBCT(t=2.531,P=0.018),IGTV3D与IGTVCBCT总匹配指数为(0.604±0.0430),亚组胸中段食管癌IGTV3D与IGTVCBCT匹配指数为(0.611±0.0371),胸下段食管癌IGTV3D与IGTVCBCT匹配指数为(0.562±0.0168),胸中段与胸下段食管癌IGTV3D与IGTVCBCT匹配指数比较,差异具有统计学意义(t=2.478,P=0.028)。结论在胸中下段食管癌的放疗中IGTV3DCT明显大于IGTVCBCT,两靶区的匹配指数为(0.604±0.0430),IGTV3DCT不能有效的包含IGTVCBCT,即使3DCT与CBCT配准校正后,也有可能导致较严重的脱靶,放疗期间利用CBCT图像不能提供可靠有效的在线校正。

Objective To compare the volume and matching index（MI） of internal gross target volume（IGTV） in thoracic middle and lower segment esophageal cancer based on three-dimensional CT（3DCT） and cone beam CT（CBCT）. Methods There were 15 patients with thoracic middle and lower segment esophageal cancer. Firstly, they received chest 3DCT scan. On the basis of their 3DCT results, radiotherapy scheme was formulated, and IGTV3 DCT was delineated. Their IGTV was gained from external expansion of 95% confidence interval in thoracic middle and lower segment esophageal cancer target volume motion range by four-dimensional CT（4DCT） in Shandong province tumor hospital. The external expansions in GTV head-foot, front-back, leftright direction were 6.0, 3.0, and 3.0 mm respectively, and IGTV3 DCT could be showed from them. CBCT was taken in the first five times of radiotherapy treatment, and it was adjusted by bone landmarks. IGTVCBCT was delineated from CBCT image. Target volumes and matching indexes were compared between IGTV3 DCT and IGTVCBCT. Results The volume of IGTV3 DCT was higher than that of IGTVCBCT（t=2.531, P=0.018）. The total matching index of IGTV3 DCT and IGTVCBCT was（0.604±0.0430）. The matching index of IGTV3 DCT and IGTVCBCT in subgroup of thoracic middle segment esophageal cancer was（0.611±0.0371）, and that of IGTV3 DCT and IGTVCBCT in thoracic lower segment esophageal cancer was（0.562±0.0168）. Difference of matching index of IGTV3 DCT and IGTVCBCT between thoracic middle and lower segment esophageal cancer had statistical significance（t=2.478, P=0.028）. Conclusion In the radiotherapy for thoracic middle and lower segment esophageal cancer, IGTV3 DCT is obviously higher than IGTVCBCT, and their matching index was（0.604±0.0430）. Therefore, IGTV3 DCT cannot effectively contain IGTVCBCT. Even through registration correction of 3DCT and CBCT, possibility of severe offtarget still exists. CBCT image cannot provide reliable online correction in radiotherapy.