18F-FAPI PET/CT performs better in evaluating mediastinal and hilar lymph nodes in patients with lung cancer: comparison with 18F-FDG PET/CT

Background The aim of this study was to evaluate the efficacy of fluorine 18 (.sup.18F) labeled fibroblast activation protein inhibitor (FAPI) in identifying mediastinal and hilar lymph node metastases and to develop a model to quantitatively and repeatedly identify lymph node status. Methods Twenty-seven patients with 137 lymph nodes were identified by two PET/CT images. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of lymph node status were analyzed, and the optimal cut-off value was identified by ROC analysis. Results The SUVmax of metastatic lymph nodes on .sup.18F-FAPI was higher than that on .sup.18F-FDG PET/CT (10.87 [+ or -] 7.29 vs 6.08 [+ or -] 5.37, p < 0.001). .sup.18F-FAPI presented much greater lymph node detection sensitivity, specificity, accuracy, PPV and NPV than .sup.18F-FDG PET/CT (84% vs. 71%; 92% vs. 67%; 90% vs. 69%, 84% vs. 52%, and 92% vs. 83%, respectively). Additionally, the diagnostic effectiveness of .sup.18F-FAPI in small lymph nodes was greater than that of .sup.18F-FDG PET/CT (specificity: 96% vs. 72%; accuracy: 93% vs. 73%; PPV: 77% vs. 33%, respectively). Notably, the optimal cut-off value for specificity and PPV of .sup.18F-FAPI SUVmax was 5.3; the optimal cut-off value for sensitivity and NPV was 2.5. Conclusion .sup.18F-FAPI showed promising diagnostic efficacy in metastatic mediastinal and hilar lymph nodes from lung cancer patients, with a higher SUVmax, especially in small metastatic nodes, compared with .sup.18F-FDG. In addition, this exploratory work recommended optimal SUVmax cutoff values to distinguish between nonmetastatic and metastatic lymph nodes, thereby advancing the development of image-guided radiation. Trial registration ClinicalTrials.gov identifier: ChiCTR2000036091. Keywords: .sup.18F-FAPI PET/CT, Mediastinal and hilar lymph node, Lung cancer, .sup.18F-FDG PET/CT