Comparison of urinary bladder activity from [68Ga]Ga-PSMA-11 and [18F]PSMA-1007 in patients with prostate cancer undergoing PSMA-ligand PET/CT

PET/CT with radiolabelled PSMA-ligands has become the mainstay of diagnostic imaging for prostate cancer. The several available PSMA tracers differ modestly with respect to their avidity for lesions, but show distinct patterns of off-target uptake and routes of excretion. We sought to compare urinary bladder activity from [68Ga]Ga-PSMA-11 and [18F]PSMA-1007 with regard to their differing renal elimination, which can interfere in the detection of perivesical lesions. We retrospectively compared urine activity in patients undergoing PET/CT after injection of either [68Ga]Ga-PSMA-11 patients in combination with hydration and diuresis (n = 132) or [18F]PSMA-1007 patients without hydration and diuresis (n = 100). Furthermore, we compared urinary bladder uptake from [18F]PSMA-1007 with lesional uptake in locally recurrent prostate cancer and locoregional lymph node metastasis, and performed an exploratory analysis of urine activity from [18F]PSMA-1007 relative to patient characteristics. Urine activity from [68Ga]Ga-PSMA-11 was normally distributed, being lowest in acquisitions 90 min p.i. with oral hydration and a single dose of furosemide injected 60 min after the tracer. In contrast, urine activity from [18F]PSMA-1007 followed an exponential distribution in the population, with approximately one quarter of cases exceeding an SUVmean threshold of 7. Urine activity of [18F]PSMA-1007 exceeded the uptake in prostate cancer lesions in more than 20% of patients. Urinary uptake from [18F]PSMA-1007 was in the range of that seen in [68Ga]Ga-PSMA-11 patients with hydration and diuretics. Some 25% of the [18F]PSMA-1007 cases showed problematic urinary uptake, which would potentially eclipse the uptake in prostate cancer lesions.