Dual-tracer PET/CT protocol with [F]FDG and [Ga]Ga-FAPI-46 outperforms single-tracer PET/CT with [F]FDG in different cancer types, resulting in larger functional and gross tumor volume.

PURPOSE

Fibroblast activation protein (FAP) detected by positron-emission tomography (PET) using fibroblast activation protein inhibitor (FAPI) appears to be a promising target for cancer imaging, staging, and therapy, providing added value and strength as a complement to [F]fluorodeoxyglucose (FDG) in cancer imaging. We recently introduced a combined single-session/dual-tracer protocol with [F]FDG and [Ga]Ga-FAPI for cancer imaging and staging. Malignant tissue visualization and target-to-background uptake ratios (TBRs) as well as functional tumor volume (FTV) and gross tumor volume (GTV) were assessed in the present study with single-tracer [F]FDG PET/computed tomography (CT) and with dual-tracer [F]FDG&[Ga]Ga-FAPI-46 PET/CT.

METHODS

A total of 19 patients with head and neck and gastrointestinal cancers received initial [F]FDG-PET/CT followed by dual-tracer PET/CT after additional injection of [Ga]Ga-FAPI-46 during the same medical appointment (on average 13.9 ± 12.3 min after injection of [F]FDG). Two readers visually compared detection rate of malignant tissue, TBR, FTV, and GTV for tumor and metastatic tissue in single- and dual-tracer PET/CT.

RESULTS

The diagnostic performance of dual-tracer compared to single-tracer PET/CT was equal in 13 patients and superior in 6 patients. The mean TBRs of tumors and metastases in dual-tracer PET/CTs were mostly higher compared to single-tracer PET/CT using maximal count rates (CRmax). GTV and FTV were significantly larger when measured on dual-tracer compared to single-tracer PET/CT.

CONCLUSION

Dual-tracer PET/CT with [F]FDG and [Ga]Ga-FAPI-46 showed better visualization due to a generally higher TBR and larger FTV and GTV compared to [F]FDG-PET/CT in several tumor entities, suggesting that [Ga]Ga-FAPI-46 provides added value in pretherapeutic staging.