Impact of dual tracer study to differentiate malignant versus benign peritoneal diseases

F¹⁸ - FDG PET CT scan was the standard imaging modality for detecting peritoneal diseases . Lilan Fu, Shun Huang et al. showed that the sensitivity for peritoneal detection is around 93.2% by FAPI vs 53.8% by FDG. Aim: we aim to look for the utility of dual tracer study to differentiate benign from malignant pathologies. Results were grouped into 4 categories based on quantification marker SUV (maximum standardized uptake value). Category I: likely benign (FDG positive & FAPI negative or both negative), II : Probably benign (both positive but the SUV of FAPI is ≤ 50% of SUV of FDG), III: indeterminate (both positive with SUV of FAPI ranging from 50-70 % of SUV of FDG), IV: likely malignant (both positive with SUV of FAPI >70% of SUV of FDG or only FAPI positive). 30 patients who had indeterminate findings in F¹⁸ FDG PET CT scan. 6/30 patients in this category, of which 3 (3/6) were malignant histopathologies including serous cyst-adenocarcinoma ovary and endometrial carcinoma and rest 3 (3/6 ) were benign (tubercular and inflammatory). FAPI-46 PET CT scan also helped in effectively detecting primary mitotic lesions in 4/14 patients with histopathology of adenocarcinoma colon, stomach and ovaries. Rest 8/14 patients had positive findings in both the scans, with 2 (2/8) patients positive for residual disease post-surgery, 2 (2/8) with proven recurrent peritoneal disease and remaining 4/(4/8 ) patients were treatment naive. we found neither FAPI -46 nor FDG were absolutely tumor specific. But it is already proven that Ga⁶⁸ FAPI-46 PET CT scan has definitely surpassed F ¹⁸FDG PET CT scan in case of sensitivity. In this study, we have found that using dual tracer helped in differentiating benign from malignant thereby, reducing false positive and negative rates in peritoneal diseases