An Explorative Study of the Incidental High Renal Excretion of [(18)F]PSMA-1007 for Prostate Cancer PET/CT Imaging

SIMPLE SUMMARY: Prostate cancer is one of the most dominant cancers in the Western world. In recent years, the use of positron emission tomography (PET) targeting prostate-specific membrane antigen (PSMA) to image prostate cancer allows accurate diagnosis and staging. Compared to the recently registered PET tracers [(68)Ga]Ga-PSMA-11 and [(18)F]DCFPyL, [(18)F]PSMA-1007 is predominantly excreted by the hepatobiliary tract, resulting in much lower urinary uptake. This allows for an improved evaluation of the pelvic area. However, on some occasions, clinicians do observe high excretion of [(18)F]PSMA-1007 by the renal system. Yet, this sudden differential metabolism of [(18)F]PSMA-1007 remains poorly understood. In this retrospective study, we aimed to elucidate the incidental high urinary uptake of [(18)F]PSMA-1007 by assessing the individual patient characteristics, scan (data) and peptide batches. ABSTRACT: Positron emission tomography (PET) of prostate-specific membrane antigen (PSMA) allows for accurate diagnosis and staging of prostate cancer (PCa). Compared to other PSMA PET tracers available, [(18)F]PSMA-1007 is predominantly excreted via the hepatobiliary tract resulting in low renal excretion which improves evaluation of the pelvic area. However, some patients do show high urinary uptake of [(18)F]PSMA-1007. The present study aimed to investigate this sudden high urinary uptake of [(18)F]PSMA-1007 by evaluating [(18)F]PSMA-1007 PET scans from PCa patients. In this single-center retrospective study, patients that underwent [(18)F]PSMA-1007 PET imaging between July 2018 and January 2021 were included. Data regarding the individual patient characteristics, scan acquisition and batch production were analyzed. To determine the urinary excretion of [(18)F]PSMA-1007, a region of interest was drawn in the bladder, and standardized uptake values (SUVs) were calculated and compared to SUVs in the prostate. An SUVmax of >10 was considered high urinary excretion, an SUVmax 7.5–10 intermediate and an SUVmax < 7.5 low urinary excretion. A total of 344 patients underwent [(18)F]PSMA-1007 PET/CT imaging, with 37 patients receiving three or more [(18)F]PSMA-1007 PET/CT scans. The mean SUVmean and SUVmax of the bladder were 3.9 (SD 2.9) and 5.9 (SD 4.2), respectively. Fourteen percent of patients showed high urinary uptake of [(18)F]PSMA-1007. Twelve of the thirty-seven patients (32.4%) that had multiple scans showed a varying urinary uptake of [(18)F]PSMA-1007 per PSMA PET/CT scan. In terms of patient characteristics, risk factors, medication and blood laboratory results, no significant influencing variables were found. Nor was there a difference observed in the batch size and the mean radiochemical purity of PSMA-1007 for high- and low-excreting patients. However, the bladder volume affected the mean SUVmax in the bladder significantly, with higher SUVs in lower bladder volumes. In this study, we observed that a higher SUV in the urinary tract seemed to occur in patients with low bladder volume. A prospective study is needed to corroborate this hypothesis.