Comparative Analysis of Lesion Detection and Uptake Characteristics of 68Ga-FAPI PET/CT Versus 18F-FDG PET/CT in Gastric Cancer.

PURPOSE: This study aimed to compare lesion detection and uptake characteristics of 68Ga-FAPI PET/CT and 18F-FDG PET/CT in patients undergoing imaging for gastric cancer (GC) staging. METHODS: A total of 24 patients with histopathologically confirmed GC were retrospectively evaluated. All patients underwent 18F-FDG PET/CT followed by 68Ga-FAPI PET/CT within a short interval as part of their clinical staging workup. Lesion detection rates and semi-quantitative parameters, including SUVmax and tumor-to-background ratio (TBR), were compared between the two modalities. RESULTS: 68Ga-FAPI PET/CT demonstrated significantly higher SUVmax values than 18F-FDG PET/CT across primary tumors and metastatic lesions (p < 0.05). TBRs were also markedly higher for FAPI due to lower physiological background activity. In patient-based analysis, 68Ga-FAPI PET/CT identified a higher number of nodal and distant metastases compared to 18F-FDG PET/CT; however, these differences did not reach statistical significance (p = 0.25). Notably, discordant findings were observed in three patients, in whom lesions-particularly peritoneal and bone metastases-were detected by 68Ga-FAPI PET/CT but not by 18F-FDG PET/CT. CONCLUSION: 68Ga-FAPI PET/CT provides higher tracer uptake and improved TBR compared to 18F-FDG PET/CT in GC. Although lesion detection rates were numerically higher with FAPI, statistical significance was not reached in this cohort. These findings suggest a potential complementary role of FAPI PET/CT, particularly in detecting peritoneal and bone metastases and in cases with low FDG avidity. Larger prospective studies are warranted to clarify its clinical impact.