Preoperative Abdominal Enhanced CT, 18F-FDG PET/CT and 68Ga-FAPI PET/CT to Detect Peritoneal Carcinomatosis in High-Risk Patients With Gastric Cancer: A Prospective, Single-Center, Comparative Study

After being informed about the study and potential risks, all patients giving written informed consent will receive 68Ga-FAPI PET/CT on the 2nd day to 1st week of 18F-FDG PET/CT. On PET/CT, omentum, peritoneum, and mesenteric lesions with increased radioactive uptake are defined as suspicious peritoneal carcinomatosis. The number of these positive lesions, the maximum standardized uptake value (SUVmax), median and range will be recorded. Subsequently, the patients will undergo laparoscopic exploration, and if radical resection is assessed, radical gastrectomy (D2 lymph node dissection) will be performed. If a radical resection is not feasible, for patients with peritoneal carcinomatosis detected, one metastasis will be taken for rapid frozen diagnosis. After the peritoneal carcinomatosis is confirmed, the metastases seen under laparoscopy will be matched with the suspicious peritoneal carcinomatosis on the three preoperative imaging examinations. The intraoperative findings are used as the gold standard to compare the detection efficiency of the three imaging examinations for peritoneal carcinomatosis. Patients with unresected tumors will receive 4 cycles of conversion therapy or neoadjuvant therapy. After the treatment, 18F-FDG PET/CT and 68Ga-FAPI PET/CT will be performed again. If necessary, patients will be subjected to a second laparoscopic exploration, and radical gastrectomy (D2 lymph node dissection) will be performed for appropriate patients. If a radical resection is still not feasible, for patients with peritoneal carcinomatosis detected, biopsy of metastases will be performed if necessary.