Differential diagnosis between 18F-FDG-avid metastatic lymph nodes in non-small cell lung cancer and benign nodes on dual-time point PET/CT scan

The objective of this study was to clarify the difference of 18F-fluorodeoxyglucose (FDG) uptake kinetics between FDG-avid metastatic lymph nodes (LNs) in patients with non-small-cell lung cancer (NSCLC) and FDG-avid benign LNs associated with various etiologies on dual-time point positron emission tomography (PET)/CT scan, and to determine the optimal parameter for differentiation. The subjects were 134 FDG-avid metastatic LNs in 67 patients with NSCLC and 62 FDG-avid benign LNs in 61 patients with various lung disorders including NSCLC. PET/CT scan was performed at 2 time points (at 60 min and at 120 min) after intravenous injection of 4.4 MBq/kg 18F-FDG. The maximum standardized uptake value (SUVmax) on early and delayed scans and the percent change of SUVmax (%ΔSUVmax) were measured at each FDG-avid LN. The optimal parameter for differentiation was determined by the receiver-operating characteristic analysis. Delayed SUVmax was increased compared with early SUVmax in 114 (85.0%) FDG-avid metastatic LNs and 42 (67.7%) FDG-avid benign LNs, with significant higher delayed SUVmax than early values (7.0±5.0 vs. 5.9±3.4; P<0.0001, and 3.0±1.3 vs. 2.8±1.0; P<0.05, respectively). Early and delayed SUVmax and %ΔSUVmax in metastatic LNs were significantly higher than those in benign LNs (P<0.0001). The optimal parameter for the differentiation was the combined use of early SUVmax >3.0 or delayed SUVmax >4.0, yielding sensitivity of 88.8%, specificity of 80.6%, accuracy of 86.2%, negative predictive value of 76.9%, and positive predictive value of 90.6%. It provided better results than the use of early SUVmax >3.0 alone (P=0.019) or the optimal parameter for %ΔSUVmax (>5%) (P=0.012). However, 12 (19.3%) benign LNs were indistinguishable from metastatic LNs. Although dual-time point PET/CT scan enhances the difference of FDG uptake between FDG-avid metastatic and benign LNs and improves the differentiation when compared with a single scan, biopsy procedure may be still required for accurate assessment of LN status in patients with NSCLC and possible etiologies showing intensive FDG uptake in benign LNs. (author)