CT与MRI图像上脑转移瘤放疗靶区勾画的体积差异及其相关影响因素

Study of volume differences and related influencing factors between enhanced CT and MRI in delineation of radiotherapy targets for brain metastases

目的:回顾性分析CT增强扫描与MRI在勾画接受分次立体定向放射治疗(SRT)的非小细胞肺癌脑转移患者大体肿瘤靶区(GTV)时的体积差异,并分析相关影响因素,以期提高MRI-CT图像融合技术缺失时脑转移瘤GTV勾画的精确度。方法:收集因非小细胞肺癌脑转移接受SRT的33例患者(131个脑转移瘤)的影像资料,33例放疗定位CT扫描前10 d内完成头颅MRI增强扫描,将CT与MRI图像导入Elekta-Monaco治疗计划系统,分别在CT与MRI增强扫描图像上勾画131个脑转移瘤的GTV,并由计划系统生成其体积值。比较2种勾画方式下GTV的体积差异,并分析瘤周水肿、转移瘤强化类型等因素与GTV体积差异的相关性。结果:103个(78.6%)脑转移瘤在CT图像上勾画的GTV小于MRI(中位偏差度-29.60%),28个(21.4%)大于MRI(中位偏差度11.24%)。GTV的体积差异与瘤周水肿及转移瘤强化类型有关。瘤周水肿会显著增加这种差异[(-1.024±0.370)cm^(3) vs.(-0.135±0.070)cm^(3),P=0.017]。3种强化类型的脑转移瘤(环形、均匀和结节样强化)GTV偏差值差异有统计学意义(P=0.036);结节样强化脑转移瘤与均匀强化转移瘤的GTV偏差值比较,差异有统计学意义(P=0.010);结节性强化与环形强化、环形强化与均匀强化的脑转移瘤间比较,GTV偏差值的差异均无统计学意义(均P>0.05)。结论:大多数脑转移瘤在CT图像上勾画的GTV体积较MRI偏小,无瘤周水肿及强化类型为环形强化、均匀强化的脑转移瘤GTV体积差异较小,而伴瘤周水肿和/或结节样强化的GTV体积差异显著增大;提示在缺少准确的图像融合技术辅助时,应注意伴瘤周水肿和/或结节样强化脑转移瘤GTV勾画精确性较差的风险。

Objective:A retrospective analysis of the delineation difference in gross tumor volume(GTV)of brain metastatic tumors in patients with non-small cell lung cancer(NSCLC)who received stereotactic radiotherapy(SRT)between enhanced CT and MRI was performed,and the factors were analyzed.The aim is to provide new references for improving the accuracy of GTV delineation when MRI-CT image fusion technology is absent.Methods:One hundred thirty-one brain metastatic tumors from 33 NSCLC patients who had previously received SRT were included.The metastatic tumors were delineated on CT and MRI images(which were scanned within 10 d before CT)to obtain the GTV index by Elekta-Monaco treatment planning system.The volume difference was compared,and the impact factors,such as peritumoral brain edema(PTBE)and enhancement patterns,were analyzed.Results:103 metastatic tumors(78.6%)had smaller GTV on CT than on MRI(the median deviation degree of-29.6%),and 28 metastatic tumors(21.4%)had larger GTV on CT than on MRI(the median deviation degree of 11.24%).The GTV difference was associated with PTBE and the enhancement pattern.The presence of PTBE significantly increased this difference[(-1.024±0.370)cm^(3) vs.(-0.135±0.070)cm^(3),P=0.017].The GTV deviation degree difference of the three enhancement pattern(ring,homogeneous and nodular enhancement)showed a significant difference(P=0.036).The GTV deviation degree difference of nodular enhancement was statistically significant compared with the homogeneous enhancement metastatic tumor(P=0.010);the GTV deviation degree difference of ring enhancement had no statistical differences compared with that of nodular and homogeneous enhancement(both P>0.05).Conclusions:Most metastatic tumor GTV delineated on CT are smaller than those on MRI.The metastatic tumors without PTBE and with ring or homogeneous enhancement show a relatively small GTV difference,while the difference significantly increases in metastatic tumors with PTBE and/or nodular enhancement.The results suggest that particular attention should be given to such metastatic tumors for the risk of poor GTV accuracy when accurate fusion technology is absent.