Ga-PSMA-11 PET/CT in prostate cancer patients with biochemical recurrence after radical prostatectomy and PSA <0.5 ng/ml. Efficacy and impact on treatment strategy.

PURPOSE

The primary aim of this retrospective, single-centre analysis was to assess the performance of Ga-PSMA-11 PET/CT in prostate cancer (PCa) patients in early PSA failure after radical prostatectomy (RP). The secondary aim was to assess the potential impact of Ga-PSMA-11 PET/CT on treatment strategy.

METHODS

Ga-PSMA-11 PET/CT is performed in our institution within an investigational new drug (IND) trial in PCa patients with biochemical recurrence (BCR). The records of all patients enrolled between March 2016 and July 2017 were evaluated. These records were retrospectively analysed according to the following inclusion criteria: (a) RP as primary therapy, (b) proven BCR, ©) PSA levels in the range 0.2-0.5 ng/ml at the time of the Ga-PSMA-11 PET/CT investigation, and (d) no salvage radiotherapy (S-RT) performed after recurrence. The performance of Ga-PSMA-11 PET/CT was evaluated in terms of detection rate on a per-patient and a per-region basis (local vs. distant lesions). We further performed an intention-to-treat (ITT) analysis. The patient cohort was grouped into three subpopulations, blinded to the Ga-PSMA-11 PET/CT results, according to the patients' characteristics and different patterns of treatment: (1) S-RT (with or without systemic treatment), (2) stereotactic body radiotherapy (SBRT) (with or without systemic treatment), and (3) systemic treatment. The treatment strategy was re-evaluated for each patient taking into consideration the Ga-PSMA-11 PET/CT images.

RESULTS

We enrolled 119 PCa patients (mean age 66 years, range 44-78 years) with a mean PSA level at the time of Ga-PSMA-11 PET/CT of 0.34 ng/ml (median 0.32 ng/ml, SD ±0.09, range 0.20-0.50 ng/ml). Ga-PSMA-1 1 PET/CT was positive in 41 of the 119 patients, resulting in an overall detection rate of 34.4%. Ga-PSMA-11 uptake was observed in the prostate bed (3 patients, 2.5%), in the pelvic lymph nodes (21, 17.6%), in the retroperitoneal lymph nodes (4, 3.4%) and in the skeleton (21, 17.6%). Regarding ITT, 81 patients (68.1%) were considered possible candidates for S-RT only in the prostate bed and none of the patients (0%) for SBRT. According to the Ga-PSMA-11 PET/CT results, the intended treatment was changed in 36 patients (30.2%). According to the PET/CT results, S-RT was recommended in 70 patients (58.8%), only to the prostate bed in 58 (48.7%) and SBRT in 29 (24.4%). The intended RT planning was modified in 36 (87.8%) of 41 patients with a positive Ga-PSMA-11 PET/CT result.

CONCLUSION

In our patient series with PSA levels <0.5 ng/ml, Ga-PSMA-11 PET/CT had a detection rate of 34.4%. In the ITT analysis, 30.2% of patients had a change in the intended treatment. These data support the hypothesis that Ga-PSMA-11 PET/CT is a useful procedure in the management of PCa patients showing early recurrence after RP, and should be implemented in routine clinical practice.