Comparison of 68Ga-FAPI and 18F-FDG PET/CT in the Evaluation of Advanced Lung Cancer

Background Gallium 68 (⁶⁸Ga)-labeled fibroblast-activation protein inhibitor (FAPI) has recently been introduced as a promising tumor imaging agent. Purpose To compare ⁶⁸Ga-FAPI PET/CT with fluorine 18 (¹⁸F)-labeled fluorodeoxyglucose (FDG) PET/CT in evaluating lung cancer. Materials and Methods In this prospective study conducted from September 2020 to February 2021, images from participants with lung cancer who underwent both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT examinations were analyzed. The tracer uptakes, quantified by maximum standardized uptake value (SUV_max) and target-to-background ratio (TBR), were compared for paired positive lesions between both modalities using the paired t test or Wilcoxon signed-rank test. Results Thirty-four participants (median age, 64 years [interquartile range: 46-80 years]; 20 men) were evaluated. From visual evaluation, ⁶⁸Ga-FAPI PET/CT and ¹⁸F-FDG PET/CT showed similar performance in the delineation of primary tumors and detection of suspected metastases in the lungs, liver, and adrenal glands. The metabolic tumor volume in primary and recurrent lung tumors showed no difference between modalities (mean: 11.6 vs 10.8, respectively; P = .68). However, compared with ¹⁸F-FDG PET/CT, ⁶⁸Ga-FAPI PET/CT depicted more suspected metastases in lymph nodes (356 vs 320), brain (23 vs 10), bone (109 vs 91), and pleura (66 vs 35). From semiquantitative evaluation, the SUV_max and TBR of primary or recurrent tumors, positive lymph nodes, bone lesions, and pleural lesions at ⁶⁸Ga-FAPI PET/CT were all higher than those at ¹⁸F-FDG PET/CT (all P < .01). Although SUV_max of ⁶⁸Ga-FAPI and ¹⁸F-FDG in brain metastases were not different (mean SUV_max: 9.0 vs 7.4, P = .32), TBR was higher with ⁶⁸Ga-FAPI than with ¹⁸F-FDG (mean: 314.4 vs 1.0, P = .02). Conclusion Gallium 68-labeled fibroblast-activation protein inhibitor PET/CT may outperform fluorine 18-labeled fluorodeoxyglucose PET/CT in staging lung cancer, particularly in the detection of metastasis to the brain, lymph nodes, bone, and pleura. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Jacobson and Van den Abbeele in this issue.