The impact of preliminary patient hydration on physiological [18F]PSMA-1007 uptake in the urinary bladder on PET/CT

Оne of the most commonly used fluorine‑18 labeled prostate-specific membrane antigen (PSMA) ligands in positron emission tomography combined with computed tomography (PET/CT) is [ 18 F]PSMA‑1007. In comparison to other clinically available PSMA radioligands characterized by renal clearance, [ 18 F]PSMA‑1007 exhibits predominantly hepatobiliary excretion. It allows a better assessment of the pelvic area in patients with prostate cancer (PCa). Nevertheless, in our clinical practice, we routinely observed a notably high [ 18 F]PSMA‑1007 uptake in the urinary bladder. The underlying reasons for this phenomenon remain inadequately explored. Purpose of the study . The purpose of this study was to assess the impact of preliminary hydration of patients on [ 18 F]PSMA‑1007 uptake in the urinary bladder. Materials and methods. Prospective, multicenter, randomized controlled study included 180 patients with PCa who underwent [ 18 F]PSMA‑1007 PET/CT. Scans were performed using three different PET/CT-systems: GE Discovery IQ Gen 2 (USA), Siemens Biograph 64 mCT and Biograph 64 TruePoint (Germany). All patients were divided into two groups: the group with hydration ( n = 95, 53 %), which included the subgroups of patients with oral ( n = 76, 80 %) and intravenous ( n = 19, 20 %) routes of hydration, and the control group with no hydration ( n = 85, 47 %). [ 18 F]PSMA‑1007 uptake in the urinary bladder was quantified using SUVmean (Mean Standardized Uptake value), measured within a spherical VOI with a fixed volume of 2.5 cm3 delineating the bladder boundaries. Additionally, the TBRmean (Mean Target-to-Background Ratio), reflecting the ratio between urinary bladder and right gluteal muscles SUVmean. Results . SUVmean and TBRmean in urinary bladder were significantly lower ( p < 0,001) in the group with hydration compared to the control group, with the following values: 1.3 [0.8; 2.0] versus 4.5 [2.7; 8.5] for SUVmean and 4.0 [2.3; 6.3] versus 13.0 [7.7; 24.0] for TBRmean. There was no significant differences in SUVmean and TBRmean between the subgroups with oral and intravenous routes of hydration ( p = 0.95 for SUVmean, p = 0.49 for TBRmean). Additionally, comparatively lower interquartile range (IQR) values for both SUVmean and TBRmean in the group with hydration were noted: 1.2 versus 5.8 for SUVmean, 4.0 versus 16.3 for TBRmean. Conclusion . Preliminary hydration of patients in uptake period significantly reduces both the level and variability of [ 18 F]PSMA‑1007 uptake in the urinary bladder.