Mass Dose Effects in FAP-Directed Imaging: Influence of Administered Dose of [ 68 Ga]Ga-LNTH-1363S on Image Quality

Recent advances in fibroblast activation protein imaging have led to the development of new fibroblast activation protein–targeting radiotracers. This study investigates the mass dose effects of [⁶⁸Ga]Ga-LNTH-1363S on image quality. Methods: In this retrospective evaluation of 39 patients with various oncologic diseases (including breast cancer and sarcoma), different administered mass doses (30, 75, 90, and 100 μg) of [⁶⁸Ga]Ga-LNTH-1363S were visually and quantitatively (blood pool SUV_mean, lesion SUV_max, and tumor–to–blood pool ratios [TBRs]) assessed. Results: Lower peptide masses were associated with prominent blood pooling in [⁶⁸Ga]Ga-LNTH-1363S PET imaging and reduced TBRs, whereas higher mass doses yielded superior image quality because of lower mean tracer accumulation in the blood pool and therefore higher TBRs. Conclusion: These observations provide evidence that biodistribution and imaging quality are dependent on the administered mass dose. Further studies are warranted to validate these findings.