Early PET imaging with [68]Ga-PSMA-11 increases the detection rate of local recurrence in prostate cancer patients with biochemical recurrence.

Purpose: PET/CT using Ga-labelled prostate-specific membrane antigen PSMA-11 (HBEDD-CC) has emerged as a promising imaging method in the diagnostic evaluation of prostate cancer (PC) patients with biochemical recurrence. However, assessment of local recurrence (LR) may be limited by intense physiologic tracer accumulation in the urinary bladder on whole-body scans, normally conducted 60 min post-tracer injection (p.i.). It could be shown on early dynamic imaging studies that Ga-PSMA-11 uptake in PC lesions occurs earlier than tracer accumulation in the urinary bladder. This study aims to investigate whether early static PET acquisition increases detection rate of local recurrence on Ga-PSMA-11 PET/CT in comparison to PET imaging 60 min p.i..

Methods: 203 consecutive PC patients with biochemical failure referred to Ga-PSMA-11 PET/CT were analysed retrospectively (median prostate specific antigen (PSA) value: 1.44 ng/ml). In addition to whole-body PET/CT scans 60 min p.i., early static imaging of the pelvis was performed, starting at a median time of 283 s p.i. (range: 243-491 s). Assessment was based on visual analysis and calculation of maximum standardized uptake value (SUV) of pathologic lesions present in the pelvic area found on early PET imaging and on 60 min-PET scans.

Results: 26 patients (12.8%) were judged positive for LR on PET scans 60 min p.i. (median SUV: 10.8; range: 4.7-40.9), whereas 50 patients (24.6%) revealed a lesion suggestive of LR on early PET imaging (median SUV: 5.9; range: 2.9-17.6), resulting in a significant rise in detection rate (p < 0.001). Equivocal findings on PET scans 60 min p.i. decreased significantly with the help of early imaging (15.8% vs. 4.5% of patients; p < 0.001). Tracer activity in the urinary bladder with a median SUV of 8.2 was present in 63 patients on early PET scans (31.0%). However, acquisition starting time of early PET scans differed significantly in the patient groups with and without urinary bladder activity (median starting time of 321 vs. 275 s p.i.; range: 281-491 vs. 243-311 s p.i.; p < 0.001). Median SUV value of lesions suggestive of LR on early images was significantly higher in comparison to gluteal muscle, inguinal vessels and seminal vesicle/anastomosis (median SUV: 5.9 vs. 1.9, 4.0 and 2.4, respectively).

Conclusions: Performance of early imaging in Ga-PSMA-11 PET/CT in addition to whole-body scans 60 min p.i. increases the detection rate of local recurrence in PC patients with biochemical recurrence. Acquisition of early PET images should be started as early as 5 min p.i. in order to avoid disturbing tracer activity in the urinary bladder occuring at a later time point.