Influence of fasting prior to 18F-rhPSMA-7.3 (Flotufolastat F-18) PET/CT on biodistribution and tumor uptake

Glutamate is an amino acid which is synthesized by the human body and found in various foods.As it has been described as a substrate of PSMA [8], some institutions recommended fasting to prevent potential interference with ligand binding and thus diagnostic performance [8].An intense PSMA-ligand uptake is typically observed in lacrimal, parotid and submandibular glands and in the small intestine [9,10].High oral intake of monosodium glutamate has been described to substantially lower the signal in 68 Ga-PSMA11 PET of tumor lesions and salivary glands [11].Dietary restrictions can be straining, especially for patients with concomitant diseases or in poor general condition due to their underlying disease.In addition, long waiting times before the actual scan and dietary restrictions can be problematic for patients, especially the elderly.Currently, in contrast with FDG (fluordeoxyglucose) PET where fasting is essential in clinical routine, patients are not required to fast prior to PSMA-ligand PET.However, there is only limited data available on the impact of fasting vs. non-fasting on PSMA-ligand .In this retrospective analysis we investigated whether fasting prior to PET imaging with 18 F-rhPSMA-7.3(Flotufolastat F-18) substantially impacts physiologic organ and tumor uptake.