Ga-68-FAPI-04 PET for Surveillance of Anastomotic Recurrence in Postoperative Patients with Gastrointestinal Cancer: a Comparative Study with F-18-FDG PET

Purpose This study aims to compare the diagnostic efficacy of Ga-68-FAPI-04 PET and F-18-FDG PET for detecting anastomotic recurrence in postoperative patients with gastrointestinal cancer, and to characterize the signal pattern over time at surgical wounds on both PET imaging. Methods Gastrointestinal cancer patients who planned to Ga-68-FAPI-04 and F-18-FDG PET/CT imaging for postoperative surveillance were involved. The SUVmax at surgical wounds were assessed. Endoscopic pathology confirmed anastomotic recurrence or it was ruled out by imaging and clinical follow-up. The sensitivity, specificity, positive and negative predictive values (PPV and NPV), and accuracy of the two PET imaging in detecting anastomotic recurrence were compared. Relationships between tracer uptake at surgical wounds and postoperative time were also analyzed. Results Compared with non-recurrent patients, the recurrent patients exhibited a significantly higher anastomotic SUVmax on Ga-68-FAPI-04 PET (SUVmax: 9.92 +/- 4.36 vs. 2.81 +/- 1.86, P = 0.002). Sensitivity, specificity, PPV, NPV, and accuracy of detecting anastomotic recurrence were 100.0%, 87.3%, 41.7%, 100.0%, and 88.3% for Ga-68-FAPI-04 PET, and 60.0%, 81.8%, 23.1%, 95.7%, and 80.0% for F-18-FDG PET, respectively. Although Ga-68-FAPI-04 PET signal at surgical wounds showed a slight trend to decrease with time, no statistical difference was observed over months post-surgery (P > 0.05). Conclusions Both tracers displayed high NPVs in identifying anastomotic recurrence with a higher sensitivity to Ga-68-FAPI-04. Tracer uptake at anastomotic sites does not decrease significantly over time, which results in low PPVs for both PET. Therefore, it is difficult to differentiate anastomotic recurrence from inflammation on either PET imaging.