基于4DCT探讨放疗中食管癌GTV50及IGTV空间位置及重合度变化

目的 基于4DCT模拟定位增强扫描探讨放疗不同时段胸段食管癌GTV₅₀、IGTV空间位置及重合度变化。方法 对33例胸段食管癌患者于放疗前及放疗10次、20次时行4DCT模拟定位增强扫描,分别在每次扫描各时相图像上勾画食管癌GTV₅₀并构建IGTV。比较不同时段靶体积大小、DI和MI。结果 疗程中GTV₅₀、IGTV体积均呈递减趋势,两靶区中心点位置变化均不明显。初始靶区对放疗10次、20次GTV₅₀的DI分别为0.75、0.63(P=0.000),IGTV的分别为0.79、0.66(P=0.000);GTV₅₀的MI分别为0.61、0.56(P=0.002),IGTV的分别为0.68、0.58(P=0.005)。两靶体积比变化与初始各靶区对疗程中各靶区DI变化均呈正相关(r=0.632,r=0.783),与MI亦均呈正相关(r=0.387,r=0.483),三维运动矢量与MI均呈负相关(r=－0.455,r=－0.438)。结论 胸段食管癌原发灶常规剂量分割放疗时GTV₅₀、IGTV空间位置变化均<0.8 cm,同时放疗中靶区退缩致使靶区DI及MI出现不同程度下降。

Variations of spatial position and overlap ratio for GTV50 and IGTV of primary thoracic esophageal cancer during radiotherapy:a study based on 4DCT scans

Objective To investigate the variations of the spatial position and overlap ratio for gross tumor volume (respiratory phase 50%)(GTV₅₀) and internal gross tumor volume (IGTV) of primary thoracic esophageal cancer during conventional fractionated radiotherapy based on repeated four-dimensional computed tomography (4DCT) scans. Methds Thirty-three patients with thoracic esophageal cancer underwent contrast-enhanced 4DCT scans before radiotherapy and at the 10^th and 20^th fractions of radiotherapy. Scans were registered to the baseline 4DCT scan using bony landmarks. The GTV₅₀ was delineated by the same radiotherapist on each 4DCT imaging data set, and the IGTV was constructed accordingly. The target volume, degree of inclusion (DI), and matching index (MI) were compared in different phases. Results The volumes of GTV₅₀ and IGTV decreased along with treatment course. No significant changes in the centroid position were observed for the GTV₅₀ and IGTV. The median DIs of the target volumes at the 10^th and 20^th fractions in the original target volume were 0.75 and 0.63(P=0.000) for GTV₅₀ and were 0.79 and 0.66(P=0.000) for IGTV, while the median MIs were 0.61 and 0.56(P=0.002) for GTV₅₀ and were 0.68 and 0.58(P=0.005) for IGTV. A positive correlation between the variation of volume ratio and the variation of DI was found for GTV₅₀ and IGTV (r=0.632, r=0.783), and the variation of volume ratio was also positively correlated with the variation of MI (r=0.387, r=0.483);the 3D vector was negatively correlated with the MI (r=－0.455, r=－0.438). Conclusions During conventional fractionated radiotherapy, the variation of spatial position is less than 0.8 cm for GTV₅₀ and IGTV of primary thoracic esophageal cancer, and the decline of the target leads to varying degrees of decreases in DI and the MI.