Early dynamic imaging in 68Ga- PSMA-11 PET/CT allows discrimination of urinary bladder activity and prostate cancer lesions.

Abstract

PET/CT with 68Ga-labelled prostate-specific membrane antigen (PSMA)-ligands has been proven to establish a promising imaging modality in the work-up of prostate cancer (PC) patients with biochemical relapse. Despite a high overall detection rate, the visualisation of local recurrence may be hampered by high physiologic tracer accumulation in the urinary bladder on whole body imaging, usually starting 60min after injection. This study sought to verify whether early dynamic 68Ga-PSMA-11 (HBED-CC)PET/CT can differentiate pathologic PC-related tracer uptake from physiologic tracer accumulation in the urinary bladder. Eighty consecutive PC patients referred to 68Ga -PSMA-11 PET/CT were included in this retrospective analysis (biochemical relapse: n = 64; primary staging: n = 8; evaluation of therapy response/restaging: n = 8). In addition to whole-body PET/CT acquisition 60min post injection early dynamic imaging of the pelvis in the first 8min after tracer injection was performed. SUVmax of pathologic lesions was calculated and time-activity curves were generated and compared to those of urinary bladder and areas of physiologic tracer uptake. A total of 55 lesions consistent with malignancy on 60min whole body imaging exhibited also pathologic 68Ga-PSMA-11 uptake during early dynamic imaging (prostatic bed/prostate gland: n = 27; lymph nodes: n = 12; bone: n = 16). All pathologic lesions showed tracer uptake within the first 3min, whereas urinary bladder activity was absent within the first 3min of dynamic imaging in all patients. Suvmax was significantly higher in PC lesions in the first 6min compared to urinary bladder accumulation (p < 0.001). In the subgroup of PC patients with biochemical relapse the detection rate of local recurrence could be increased from 20.3 to 29.7%. Early dynamic imaging in 68Ga-PSMA-11 PET/CT reliably enables the differentiation of pathologic tracer uptake in PC lesions from physiologic bladder accumulation. Performance of early dynamic imaging in addition to whole body imaging 60min after tracer injection might improve the detection rate of local recurrence in PC patients with biochemical relapse referred for 68Ga-PSMA-11 PET/CT.