Abstract
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Objectives: To evaluate the diagnostic performance of 18F-FDG PET/CT in detecting individual lymph node metastasis using Hounsfield units of lymph nodes on non-contrast CT image component and 18F-FDG uptake in patients with esophageal squamous cell carcinoma.
Methods: 203 patients with esophageal squamous cell carcinoma underwent 18F-FDG PET/CT before esophagectomy and lymph node dissection. Maximum standardized uptake value (SUVmax), mean Hounsfield unit (HU), and short axis diameters (size) were evaluated on non-contrast CT and PET images of PET/CT scan. The images were analyzed by three methods. In Method 1, nodal status was determined by FDG uptake only using cut-off values of ROC analysis. In Method 2, nodal status was determined by FDG uptake associated with mediastinal CT attenuation (70 HU). Benign lymph nodes were defined when lymph nodes with less than SUVmax of cut-off value (Method 1) or when those with a higher attenuation than 70 HU and/or containing calcifications on non-contrast CT images even if SUVmax was higher than the cut-off value. In Method 3, benign nodes were determined by the same cut-off value of SUVmax but with a higher cut-off value of HU from the ROC analysis. The sensitivity, specificity, and accuracy of each method were compared by the postoperative histologic result as a reference standard.
Results: Total 1099 nodal stations were dissected, and 949 nodal stations proved to be metastases. SUVmax and size of malignant lymph nodes were higher than those of benign nodes (p<0.001). From the ROC analyses, the cut-off value of SUVmax was 2.6, and that of CT attenuation was 80 HU. The sensitivity, specificity, and accuracy of Method 1 were 72.7 %, 76.1 %, and 75.6 %. When compared to Method 1, Method 2 and 3 showed significantly higher specificity of 91.6% and 88.6%, higher accuracy of 85.6% and 84.8%, but lower sensitivities of 48.0% and 60.7%, respectively (all, p<0.001). There was no significant difference between Method 2 and Method 3 (p=0.243).
Conclusions: The accuracy of PET/CT for nodal metastasis in esophageal squamous cell carcinoma was improved by combined interpretation of 18F-FDG uptake and CT attenuation. Enhanced specificity could lead to the determining extent of lymphadenectomy in patients with a surgical candidate of esophageal cancer. [This paper was supported by the following grant(s): The National R & D Program for Cancer Control, Ministry of Health & Welfare, Korea (1720180).]