Usefulness of [ 68 Ga]FAPI-04 and [ 18 F]FDG PET/CT for the detection of primary tumour and metastatic lesions in gastrointestinal carcinoma: a comparative study

Objective To assess and compare the diagnostic performance of gallium-68-labelled fibroblast activation protein inhibitor ([ 68 Ga]FAPI-04) and fluorine-18 fluorodeoxyglucose ([ 18 F]FDG) positron emission tomography/computed tomography (PET/CT) in gastrointestinal cancer. Methods Fifty-one patients who underwent both [ 18 F]FDG and [ 68 Ga]FAPI-04 PET/CT for initial staging or restaging were enrolled. Histopathological findings, typical radiological appearances, and clinical imaging follow-up were used as the reference standard. The diagnostic performance of the two tracers was calculated and compared. The maximum standardised uptake value (SUVmax), mean SUV (SUVmean), tumour-to-mediastinal blood pool ratio (TBR), and tumour-to-liver ratio (TLR) of primary and metastatic lesions were measured and compared between two imaging modalities. Results In patient-based analysis, [ 68 Ga]FAPI-04 showed much better diagnostic sensitivity than [ 18 F]FDG in detecting primary tumour (94.44% [17/18] vs. 61.11% [11/18]), postoperative recurrence and metastases (95.65% [22/23] vs. 69.57% [16/23]), and peritoneal carcinomatosis (100% [28/28] vs. 60.71% [17/28]) (all p < 0.05). In lesion-based analysis, [ 68 Ga]FAPI-04 showed higher sensitivity than [ 18 F]FDG for detecting lymph node metastases. In peritoneal carcinomatosis, the median SUVmax (12.12 vs. 7.18) and SUVmean (6.84 vs. 4.11) with [ 68 Ga]FAPI-04 were significantly higher than those with [ 18 F]FDG (all p < 0.005). The TBR and TLR of [ 68 Ga]FAPI-04 were significantly higher than those of [ 18 F]FDG for detecting primary tumour, lymph node, liver, and peritoneal metastases (all p < 0.005). Therapeutic management changed in 13 patients according to [ 68 Ga]FAPI-04 PET/CT compared with conventional imaging. Conclusions [ 68 Ga]FAPI-04 is superior to [ 18 F]FDG PET/CT for detecting primary tumour, postoperative recurrence and metastasis, and peritoneal carcinomatosis in gastrointestinal cancer. Key Points • [ 68 Ga]FAPI-04 PET/CT showed significantly higher sensitivity than [ 18 F]FDG PET/CT in the detection of primary tumour and postoperative recurrence and metastasis in patients with gastrointestinal carcinoma. • [ 68 Ga]FAPI-04 PET/CT had obvious advantages over [ 18 F]FDG PET/CT in the detection of peritoneal carcinomatosis from gastrointestinal carcinoma with a much higher FAPI uptake value, TBR, and TLR. • Although the median SUVmax and SUVmean of [ 68 Ga]FAPI-04 were similar to those of [ 18 F]FDG for the primary tumour, lymph node metastases, and liver metastases in gastrointestinal carcinoma, the TBR and TLR of the SUVmax and SUVmean were significantly higher on [ 68 Ga]FAPI-04 PET/CT, causing the lesions to be displayed more clearly.