Ali Afshar-Oromieh, Lars Peter Sattler, Walter Mier, Boris A. Hadaschik, Jürgen Debus, Tim Holland-Letz, Klaus Kopka, Uwe Haberkorn

While Positron Emission Tomography/Computed Tomography (PET/CT) with (68)Ga-PSMA-11 in the diagnosis of prostate cancer (PCa) is routinely performed at 1h post injection (p.i.), later scans may be beneficial since most lesions present with higher uptake and contrast. This evaluation aimed to investigate the clinical impact of additional late (68)Ga-PSMA-11-PET/CT. Between 2011 and 2016, 112 patients with PCa who received early (at 1h p.i.) and late (at 3h p.i.) (68)Ga-PSMA-11-PET/CT scans were retrospectively evaluated. The late scans were conducted in order to clarify unclear findings in early scans or to increase the probability of tumor detection in case of negative early scans. All patients were asked to drink 1 liter of water between early and late scans. In addition, 20 of them received 20 milligram furosemide prior to late scans. Tumor detection and radioactivity concentration within the urinary bladder were analyzed in both scans. The maximum standardized uptake value (SUVmax) and contrast of 149 tumor lesions were measured in 69 patients with pathological findings. Overall, 134 lesions characteristic for PCa in 57 patients clearly presented at 1h p.i. and 147 lesions in 68 patients at 3h p.i.. Forty-three patients showed no pathological findings. Eight patients (7.1%) showed one unclear finding in early scans which could be clarified as characteristic for PCa at 3h p.i.. Four patients (3.6%) presented with one lesion characteristic for PCa at 3h p.i. only. Twelve patients (10.7%) presented with 12 possible PCa lesions at 1h p.i., which, however, could not be confirmed as PCa in late scans. Two patients presented with one lesion characteristic for PCa at 1h p.i. which became invisible at 3h p.i. due to low contrast. At 3h p.i., 62.4% of the lesions demonstrated higher SUVmax and 65.1% higher contrast compared to 1h p.i. Patients with furosemide presented with lower SUV and radioactivity concentration within the urinary bladder. (68)Ga-PSMA-11-PET/CT at 3h p.i. showed most lesions characteristic for PCa with higher uptake and contrast. In addition, the radioactivity signal within the urinary bladder was lower at 3h p.i., especially when furosemide was applied. Consequently, scans at 3h p.i. detected more tumor lesions than 1h p.i.