基于CT/MRI/PET-CT进行鼻咽癌大体肿瘤区及淋巴结勾画的对照研究

A comparative study on the delineation of gross tumor volume and lymph nodes of nasopharyngeal carcinoma patients using CT/MRI/and PET-CT

目的比较基于计算机体层成像(CT)、磁共振成像(MRI)、^(18)氟-脱氧葡萄糖正电子发射计算机断层显像(^(18)F-FDG PET-CT)3种图像勾画鼻咽癌(NPC)大体肿瘤靶区(GTV)及淋巴结的差异,并以MRI为参考研究基于PET自动勾画NPC GTV的最佳标准摄取值(SUV)。方法选取拟行放疗的鼻咽癌患者53例,依次获得CT模拟定位、MRI模拟定位及PET图像,在3种图像上分别勾画GTV与阳性淋巴结,分别命名为GTV_(MRI)、GTV_(CT)、GTV_(PET2.5)(SUV=2.5)、Lymph_(MRI)、Lymph_(CT)、Lymph_(PET2.5),比较不同图像确定的GTV及淋巴结差异。将MRI与PET-CT配准后,得到相交区域GTV∩2.5,依据SUV=4.0、4.5、5.0、5.6为阈值分别在PET上自动勾画GTV_(PET4.0)、GTV_(PET4.5)、GTV_(PET5.0)、GTV_(PET5.6),比较不同GTV之间体积、相似系数(DSC)的差异。结果在3种图像中,GTV_(MRI)分别较GTV_(CT)增加了1.73%(P>0.05),较GTV_(PET2.5)减小了21.34%(t=-3.52,P<0.05);Lymph_(PET2.5)的体积分别为Lymph_(MRI)、Lymph_(CT)的1.61、1.87倍(t=-4.12、-5.18,P<0.05)。PET上表现为高摄取的淋巴结体积平均为无或低摄取的4.07倍(t=5.50,P<0.05)。GTV_(PET4.0)与GTV_(MRI)的DSC为0.78±0.27,低于GTV_(PET2.5)与GTV_(MRI)的DSC(0.84±0.18),但GTV_(PET4.0)与GTV∩2.5体积基本相当(P>0.05)。结论基于CT、MRI、^(18)F-FDG PET-CT勾画鼻咽癌GTV及淋巴结时,MRI可更好显示肿瘤边界;而基于^(18)F-FDG PET-CT自动勾画GTV时,推荐SUV=4.0作为阈值。

Objective To compare the differences in the delineation of the gross tumor volume(GTV)and lymph nodes of nasopharyngeal carcinoma(NPC)patients using computerized tomography(CT),magnetic resonance imaging(MRI),and ^(18)F-fluorodeoxyglucose positron emission tomography/computed tomography(^(18)F-FDG PET/CT),and to investigate the optimal standard uptake value(SUV;relative to the MRI-based delineation)for the automatic delineation of GTV using PET.Methods A total of 53 NPC patients proposing to receive radiotherapy were selected for this study.The CT,MRI,and PET images of each patient were obtained before radiotherapy.Then GTV and positive lymph nodes were delineated on these three types of images.They were individually named GTV_(MRI),GTV_(CT),GTV_(PET2.5)(SUV=2.5),Lymph_(MRI),Lymph_(CT),and Lymph_(PET2.5) and compared.The GTV∩2.5(overlapped GTV)was obtained through the alignment of MRI and PET/CT images.Meanwhile,GTV was delineated on PET images using thresholds of SUV=4.0,4.5,5.0,and 5.6,obtaining GTV_(PET4.0),GTV_(PET4.5),GTV_(PET5.0),and GTV_(PET5.6).Then their volume and Dice similarity coefficients(DSCs)were compared.Results Compared to GTV_(MRI),GTV_(CT) decreased by 1.73%(P>0.05)and GTV_(PET2.5) increased by 21.34%(t=-3.52,P<0.05)in the three types of images.The volume of Lymph_(PET2.5) was 1.61 and 1.87 times the volume of Lymph_(MRI) and Lymph_(CT),respectively(t=-4.12,-5.18;P<0.05).The volume of high-SUV lymph nodes was 4.07 times the volume of lymph nodes with low SUVs or SUV=0(t=5.50,P<0.05)on PET images.The DSC between GTV_(PET4.0) and GTV_(MRI) was 0.78±0.27,which was lower than that between GTV_(PET2.5) and GTV_(MRI)(0.84±0.18).However,GTV_(PET4.0) approximated to GTV∩2.5(P>0.05).Conclusions Compared to CT and ^(18)F-FDG PET/CT,MRI shows more accurate boundaries of GTV and lymph nodes.When ^(18)F-FDG PET/CT was adopted to automatically delineate GTV,the GTV delineated using SUV=4.0 was closer to GTV_(MRI).