One-stop [¹⁸F]FDG and [⁶⁸Ga]Ga-DOTA-FAPI-04 total-body PET/CT examination with dual-low activity: a feasibility study.

Abstract

Positron emission tomography/computed tomography (PET/CT) based on fibroblast activation protein inhibitors (FAPI) has shown complementary values to 2-[¹⁸F]-fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) in cancer imaging. This study aimed to investigate the feasibility of a one-stop FDG-FAPI dual-tracer imaging protocol with dual-low activity for oncological imaging. Nineteen patients with malignancies underwent one-stop [¹⁸F]FDG (0.37 MBq/kg) PET (PET_FDG) and dual-tracer PET 30-40 and 50-60 min (hereafter, PET_D30-40 and PET_D50-60, respectively) after additional injection of [⁶⁸Ga]Ga-DOTA-FAPI-04 (0.925 MBq/kg), with a single diagnostic CT to generate the PET/CT. The lesion detection rate and tumor-to-normal ratios (TNRs) of tracer uptake were compared between PET_FDG/CT and PET_D50-60/CT and between PET_D50-60/CT and PET_D30-40/CT. In addition, a visual scoring system was established to compare the lesion detectability. The dual-tracer PET_D50-60 and PET_D30-40/CT showed similar performance in detecting primary tumors but presented significantly higher lesion TNRs than PET_FDG. Significantly, more metastases with higher TNRs were identified on PET_D50-60 than PET_FDG (491 vs. 261, P < 0.001). The dual-tracer PET_D50-60 received significantly higher visual scores than single PET_FDG (111 vs. 10) in demonstrating both primary tumors (12 vs. 2) and metastases (99 vs. 8). However, these differences were not significant between PET_D50-60 and PET_D30-40. These resulted in tumor upstaging in 44.4% patients taking PET/CT for initial assessment, and more recurrences (68 vs. 7) were identified in patients taking PET/CT for restaging, both on PET_D50-60 and PET_D30-40, compared to PET_FDG. The reduced effective dosimetry per patient (26.2 ± 2.57 mSv) was equal to that of a single standard whole-body PET/CT. The one-stop dual-tracer dual-low-activity PET imaging protocol combines the strengths of [¹⁸F]FDG and [⁶⁸Ga]Ga-DOTA-FAPI-04 with shorter duration and lesser radiation and is thus clinically applicable.