Head-to-head intra-individual comparison of biodistribution and tumor uptake of (68)Ga-FAPI and (18)F-FDG PET/CT in cancer patients

PURPOSE: FAPI ligands (fibroblast activation protein inhibitor), a novel class of radiotracers for PET/CT imaging, demonstrated in previous studies rapid and high tumor uptake. The purpose of this study is the head-to-head intra-individual comparison of (68)Ga-FAPI versus standard-of-care (18)F-FDG in PET/CT in organ biodistribution and tumor uptake in patients with various cancers. MATERIAL AND METHODS: This international retrospective multicenter analysis included PET/CT data from 71 patients from 6 centers who underwent both (68)Ga-FAPI and (18)F-FDG PET/CT within a median time interval of 10 days (range 1–89 days). Volumes of interest (VOIs) were manually drawn in normal organs and tumor lesions to quantify tracer uptake by SUVmax and SUVmean. Furthermore, tumor-to-background ratios (TBR) were generated (SUVmax tumor/ SUVmax organ). RESULTS: A total of 71 patients were studied of, which 28 were female and 43 male (median age 60). In 41 of 71 patients, the primary tumor was present. Forty-three of 71 patients exhibited 162 metastatic lesions. (68)Ga-FAPI uptake in primary tumors and metastases was comparable to (18)F-FDG in most cases. The SUVmax was significantly lower for (68)Ga-FAPI than (18)F-FDG in background tissues such as the brain, oral mucosa, myocardium, blood pool, liver, pancreas, and colon. Thus, (68)Ga-FAPI TBRs were significantly higher than (18)F-FDG TBRs in some sites, including liver and bone metastases. CONCLUSION: Quantitative tumor uptake is comparable between (68)Ga-FAPI and (18)F-FDG, but lower background uptake in most normal organs results in equal or higher TBRs for (68)Ga-FAPI. Thus, (68)Ga-FAPI PET/CT may yield improved diagnostic information in various cancers and especially in tumor locations with high physiological (18)F-FDG uptake. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00259-021-05307-1.