Comparison of 18F-FDG PET/CT and 68Ga-FAPI-04 PET/CT in the staging and restaging of gastric adenocarcinoma.

Objective In this study, we aimed to evaluate the diagnostic sensitivities of 68Ga-FAPI-04 PET/CT and 18F-FDG PET/CT in the primary tumor, and nodal, peritoneal and distant organ metastases of primary and recurrent gastric adenocarcinoma (GAc) with patient and lesion-based comparison. Materials and method Twenty-one patients with histopathologically proven newly diagnosed or recurrent GAc who underwent 18F-FDG and 68Ga-FAPI-04 imaging were included in the study. Both imaging techniques were evaluated visually according to the intensity of organ-based uptake. SUVmax and tumor-to-background ratio (TBR) values obtained from primary tumor/relapse and metastatic organs were compared statistically. Results 68Ga-FAPI-04 uptake was positive in all 15 newly diagnosed patients, while two patients among them who had mucinous and signet ring cell carcinoma did not exhibit 18F-FDG uptake. The sensitivity and specificity of 68Ga-FAPI-04 PET/CT in detecting primary gastric were 100%, while the sensitivity and specificity of 18F-FDG were 86.6 and 100%, respectively. 68Ga-FAPI-04 imaging revealed diffuse stomach uptake in seven patients, while 18F-FDG could only show two of them. The sensitivity and specificity of in-patient-based detection of lymph node metastases were 100 and 95.2%, respectively, while these values were 71.4 and 93.7%, respectively, for 18F-FDG. For peritoneal involvement 68Ga-FAPI-04 had a sensitivity and specificity of 100%, whereas 18F-FDG had a sensitivity of 40% and a specificity of 100%. Conclusion 68Ga-FAPI-04 PET/CT is an imaging modality with the potential of yielding more sensitive and specific findings 18F-FDG PET/CT. This modality may help avoid invasive diagnostic procedures that may be frequently required in GAc.