Introduction

The aim of this retrospective study was to evaluate the detection rate of 68Ga-PSMA PET/CT in a homogeneous patient population with biochemical recurrent prostate cancer defined by Phoenix criteria after external beam radiotherapy (EBRT) or brachytherapy as primary treatment and who had not undergone previous salvage prostatectomy.

Methods

After screening of our institutional database 118 patients were finally eligible for this retrospective analysis with a median PSA of 6.4 ng/mL (range: 2.2 - 158.4 ng/mL). 77 and 41 patients had been treated by EBRT or brachytherapy, respectively. Of the 118 patients, 45 were receiving androgen deprivation therapy (ADT) within at least 6 months prior to 68Ga-PSMA PET/CT. The detection rates were stratified by PSA (2 to <5, 5 to <10 and ?10 ng/mL). The influence of primary Gleason score at diagnosis and ADT was assessed. Correlations between standardized uptake values (SUV) and Gleason score or ADT in patients with positive findings were analyzed.

Results

90.7% (107/118) patients showed pathological findings indicative for tumor recurrence in 68Ga-PSMA PET/CT. The detection rates were 81.8% (36/44), 95.3% (41/43) and 96.8% (30/31) for PSA ranges of 2 to <5, 5 to <10 and ?10 ng/mL, respectively. 68Ga-PSMA PET/CT indicated local recurrence in 68/107 patients (63.5%), only distant lesions in 64/105 patients (59.8%) and local recurrence as well as distant lesions in 25/107 patients (23.4%). The detection rate was significantly higher in patients with ADT (97.7%) vs. without ADT (86.3%, p=0.0381), but independent from primary Gleason score ?8 (92.0%) vs. ?7 (90.2%, p=0.6346). SUVmax and SUVmean were significantly higher in patients with ADT (p=0.0025 and 0.0044, respectively) and a clear trend to higher values was observed for patients with Gleason score ?8 (p=0.0502 and 0.0514, respectively).

Conclusions

68Ga-PSMA PET/CT demonstrates high detection rates in patients with biochemical recurrence of prostate cancer after primary radiation therapy as defined by Phoenix criteria. The detection rate positively correlated to increasing PSA as well as concomitant ADT. 68Ga-PSMA PET/CT enables discrimination of local vs. systemic disease and thus might have a crucial impact on further clinical management. The high observed detection rates even at very low PSA values questions the definition of recurrence by the current Phoenix criteria. A limitation of this study is the lack of histopathological proof in the majority of patients.

Funding

none