基于4D-CT扫描放疗中食管癌靶区空间位置及重合度的变化

Variations of the spatial position and overlap ratio for primary thoracic esophageal cancer target during radiotherapy based on four-dimensional CT scans

目的 基于四维CT（4D-CT）模拟定位扫描,探讨放疗疗程中不同时段胸段食管癌原发肿瘤内靶区及计划靶区空间位置及重合度的变化.方法 33例胸段食管癌患者,分别于放疗前及放疗10次、20次时行4D-CT模拟定位扫描,分别在每次扫描各时相图像上勾画食管癌大体肿瘤体积（GTV）,并构建内靶区（ITV）及计划靶区（PTV）.结果 放疗疗程中ITV及PTV体积均呈递减趋势,两靶区中心点位置变化均不明显.初始各靶区对疗程中各靶区包含度ITV分别为0.85、0.77（Z=-3.10,P＜0.05）,PTV为0.86、0.82（Z=-2.49,P＜0.05）.疗程中不同时段各靶区匹配指数ITV分别为0.77、0.70（Z=-3.16,P＜0.05）,PTV为0.82、0.76（Z=-2.49,P＜O.05）.疗程中ITV及PTV各自体积比值变化与其初始靶区对疗程中靶区包含度变化均呈正相关（rITV=0.71、rPTV=0.77,P＜0.05）,疗程中ITV及PTV各自体积比值变化与各自匹配指数变化呈正相关（rITV=0.47、rPTV=0.59,P＜0.05）.ITV及PTV三维运动矢量与各自匹配指数呈负相关（rITV=-0.52、rPTV=-0.36,P＜0.05）.放疗疗程中若以初始PTV制定放疗计划,则放疗10次、20次时分别有8.80％和6.37％的靶区漏照（Z=-0.55,P＞0.05）,11.45％和18.49％的正常组织受照射（Z=-2.49,P＜0.05）.结论 胸段食管癌原发肿瘤常规剂量分割放疗时,内靶区及计划靶区空间位置变化均＜0.6 cm;放疗疗程中靶区退缩致使靶区包含度及匹配指数不同程度下降,导致不同程度脱靶及正常组织受照射.

Objective To investigate the variations of the spatial position and overlap ratio of the internal target volume （ITV） and planning target volume （PTV） of primary thoracic esophagus carcinoma using repeated four-dimensional computed tomography （4D-CT） scanning during conventional fractionated radiotherapy.Methods Thirty patients with thoracic esophageal carcinoma were included whose 4D-CT scans were conducted before radiotherapy and between every ten fractions.The gross tumor volumes （GTVs） were delineated by the same radiation oncologist on each 4D-CT image phase,and the ITV and PTV were constructed afterwards.Results No significant difference of the isocenters was observed for the ITV and PTV during the treatment course,yet both the volumes of the ITV and PTV decreased.The median DI （the degree of inclusion） of the target acquired subsequently in the original target were 0.85,0.77 （Z=-3.10,P ＜0.05） for ITV and 0.86、0.82（Z =-2.49,P ＜0.05）for PTV respectively during entire treatment.The variation of volume ratio correlated strongly with the variation of DI （the DI of the target acquired subsequent in the original target） （rITV =0.71,rPTV =0.77,P ＜0.05）.The variation of volume ratio and the variation of the matching index （MI） were positively correlated （rITV =0.47,rPTV =0.59,P ＜ 0.05）.The 3D vectors of ITV and PTV motions were negatively correlated with the corresponding MI （rITV =--0.52,rPTV =-0.36,P ＜ 0.05）.If the initial PTV was used for treatment planning,8.80％ and 6.37％ of the target volume would be missed at the tenth and twentieth fraction （Z =-0.55,P ＞ 0.05）,respectively.In the meanwhile,11.45％ and 18.49％ of the normal tissues would be wrongly irradiated at the corresponding time points （Z =-2.49,P ＜ 0.05）.Conclusions The variations of the spatial position of all targets were all less than 0.6 cm.The DI and the MI of the target decrease by various degrees during the treatment course,which lead to target mispositioning and normal tissue irradiation at different levels.