Comparison of 68GA-FAPI-04 PET/CT and 18F-FDG PET/CT findings in peritonitis carcinomatosa cases.

Objective: This study was conducted to compare the diagnostic accuracy of gallium-68-radiolabeled fibroblast activation protein inhibitor (⁶⁸Ga-FAPI-04), positron emission tomography/computed tomography (PET/CT), and fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) PET/CT based on the peritoneal carcinomatosis (PC) index for detecting peritoneal metastases of various cancer types, and to evaluate the potential benefits of FAPI PET/CT in patients with peritoneal metastases.

Subjects and methods: This retrospective study included 57 patients with peritoneal metastases between November 2020 and December 2021. All patients underwent ⁶⁸Ga-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT scans within 7 days.

Results: Among the 57 patients included, 32 (56.1%) were male and the median age was 54 years (22-86 years). In the visual evaluation made from a total of 13 quadrants on the abdominopelvic peritoneal surfaces, positive findings were observed in 111 quadrants in 39 patients by ¹⁸F-FDG PET/CT and in 280 quadrants in 57 patients by ⁶⁸Ga-FAPI-04 PET/CT (P<0.001). The maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR) values of ⁶⁸Ga-FAPI-04 PET/CT for the PC lesions were significantly higher than the SUVmax and TBR values of ¹⁸F-FDG PET/CT in all patients and in all quadrants (SUVmax 6.45 vs 4.1; P<0.001; TBR 14.9 vs 6.8; P<0.001).

Conclusion: Gallium-68-FAPI-04 PET/CT showed superior sensitivity compared to ¹⁸F-FDG PET/CT in both quantitative and visual evaluations of PC. Considering the low background activity and higher specific activity uptake values, ⁶⁸Ga-FAPI-04 PET/CT helped improve diagnostic accuracy.