Dual-time point ¹⁸F-FDG PET/CT for the staging of oesophageal cancer. The best diagnostic performance by retention index for N-staging in non-calcified lymph nodes

The purpose of this study is to investigate the role of dual time point (DTP) ¹⁸F-FDG PET/CT in the staging of oesophageal cancer, especially in lymph node metastasis. A total of 35 patients with oesophageal squamous cell carcinoma who underwent surgical treatment without neoadjuvant chemotherapy were enrolled as a test set and another 19 patients were enrolled as a validation set. The DTP PET/CT scans were obtained in dual time points at 60 and 120 min each, following the administration of ¹⁸F-FDG. Visual analysis was performed and semiquantitative analysis was performed using several PET parameters such as maximal standardized uptake values (SUVmax), peak SUV (SUVpeak) and retention indexes using SUVmax (RImax) and SUVpeak (RIpeak). Primary oesophageal lesions exhibited a significant difference for SUVmax at each time point scan (ANOVA, p < 0.001). For nodal staging, a total of 276 non-calcified nodal stations of the test set were evaluated. Sensitivity, specificity and accuracy of visual analysis were 32.0% (8 of 25), 96.8% (243 of 251) and 90.9% (251 of 276) in the test set. Using ROC analysis, RImax had the largest area under the curve (AUC) to detect metastatic lymphadenopathy at the optimal cut-off value of 6% (AUC 0.853, P < 0.001) in the test set (sensitivity, specificity and accuracy; 80.0% (20 of 25), 94.8% (238 of 251) and 93.5% (258 of 276)). In the validation set (179 non-calcified nodal stations), sensitivity, specificity and accuracy of RImax at the optimal cut-off of 6% were 71.4% (5 of 7), 99.4% (171 of 172) and 98.4% (176 of 179), whereas those of visual analysis were 14.3% (1 of 7), 98.8% (170 of 172) and 95.5% (171 of 179). The best diagnostic performance of nodal staging in patients with oesophageal cancer was achieved by application of RImax with a cut-off of more than 6% on DTP ¹⁸F-FDG PET/CT with the exclusion of calcified lymph nodes. Optimal clinical management in surgically-candidate oesophageal cancer patients could be achieved using the diagnostic flow on DTP ¹⁸F-FDG PET/CT. (orig.)