One-Stop 68Ga-FAPI/18F-FDG Total-Body PET/CT Scan: More Theranostics Information Available.

Purpose: This prospective study aims to assess the feasibility of a one-stop imaging protocol using 68Ga-FAPI-04/18F-FDG dual-radiotracer with dual-low-activity for tumor imaging.

Patients And Methods: Forty patients underwent one-stop 68Ga-FAPI-04 PET (PETFAPI) and dual-radiotracer PET (PETDUAL) using a total-body PET/CT scanner with a 194-cm axial field of view. After a half-dose (0.925 MBq/kg) 68Ga-FAPI-04 PET/CT, an additional half-dose (1.85 MBq/kg) of 18F-FDG was administered for a 60-minute dynamic acquisition. PETDUAL was reconstructed at 10-minute intervals (PETD0-10, PETD10-20, PETD20-30, PETD30-40, PETD40-50, and PETD50-60). Data of lesion detectability, target-to-background ratios, tumor staging, and total radiation dose were analyzed. A target-to-liver ratio (TLR) ≥ 3 on PETFAPI was considered indicative of sufficient fibroblast activation protein expression.

Results: PETD50-60 and PETFAPI showed similar performance in detecting primary tumors (42 vs 41, P > 0.999). However, significantly more metastatic lesions were identified on PETD50-60 compared with PETFAPI (102 vs 60, P < 0.001). PETFAPI demonstrated significantly higher TLR, target-to-blood-pool ratio, and target-to-normal-tissue ratio than PETDUAL (P < 0.05). Lesion detectability was similar across PETD10-20, PETD20-30, PETD30-40, PETD40-50, and PETD50-60 (all P's > 0.05). Notably, PETD30-40 and PETD40-50 detected all lesions identified by PETD50-60. PETD40-50 showed no significant differences in TLR, target-to-blood-pool ratio, and target-to-normal-tissue ratio compared with PETD50-60 (P > 0.05). Up to 94.9% of malignant primary lesions exhibited a TLR ≥ 3 on PETFAPI. The average effective dose was 9.85 ± 2.19 mSv, similar to that of a whole-body 18F-FDG PET/CT.

Conclusions: This one-stop, dual-radiotracer, dual-low-activity imaging protocol combines the strengths of 68Ga-FAPI-04 and 18F-FDG, offering a shorter imaging duration and reduced radiation exposure.