Three-Time-Point PET Analysis of ⁶⁸Ga-FAPI-46 in a Variety of Cancers

A growing family of ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI) PET probes has shown promise in imaging a variety of medical conditions. ⁶⁸Ga-FAPI-46, in particular, has emerged as unique for both its diagnostic and its theranostic applications; however, the optimal timing of PET remains unclear. Therefore, we evaluated uptake at 3 time points after ⁶⁸Ga-FAPI-46 administration in a spectrum of tumor types. Methods: The cohort consisted of 43 patients with diverse cancer diagnoses undergoing ⁶⁸Ga-FAPI-46 PET/CT at 3 time points (10 min, 1 h, and 3 h). We determined the tracer uptake based on SUV_mean and SUV_max and on tumor-to-background-ratios (TBRs) (SUV_max/SUV_mean). Results: There were 171 lesions in the 43 patients. Comparing all lesions at different time points, the mean SUV_max was maximal at 10 min (8.2) and declined slightly at 1 h (8.15) and 3 h (7.6) after tracer administration. Similarly, the mean SUV_max log still had a similar pattern in primary lesions at 10 min, 1 h, and 3 h (n = 30; 0.98, 1.01, and 0.98, respectively), lymph node metastases (n = 37; 0.82, 0.84, and 0.81, respectively), and distant metastases (n = 104; 0.81, 0.79, and 0.74, respectively). TBR also showed nonsignificant differences at the 3 times. Conclusion: ⁶⁸Ga-FAPI-46 PET/CT imaging revealed remarkably stable tumor and background uptake as determined by SUV metrics and maintained high TBRs within 3 h of injection. Thus, it may be possible to scan with ⁶⁸Ga-FAPI-46 within 10-20 min of injection, improving workflow and decreasing patient wait times. Confirmation of these findings in a larger cohort is under way.