Impact of Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography on Prostate Cancer Salvage Radiotherapy Management: Results from a Prospective Multicenter Randomized Phase 3 Trial (PSMA-SRT NCT03582774).

BACKGROUND AND OBJECTIVE: Both imaging and several prognostic factors inform the planning of salvage radiotherapy (SRT). Prostate-specific membrane antigen positron emission tomography (PSMA-PET) can localize disease unseen by other imaging modalities. The main objective of the study was to evaluate the impact of PSMA-PET on biochemical recurrence-free survival rate after SRT. METHODS: This prospective randomized, controlled, phase 3 clinical trial randomized 193 patients with biochemical recurrence of prostate cancer after radical prostatectomy to proceed with SRT (control arm, n = 90) or undergo a PSMA-PET/computed tomography (CT) scan prior to SRT planning (investigational arm, n = 103) from June 2018 to August 2020. Any other approved imaging modalities were allowed in both arms (including fluciclovine-PET). This is a secondary endpoint analysis: impact of PSMA-PET on SRT planning. Case-report forms were sent to referring radiation oncologists to collect the management plans before randomization and after completion of SRT. The relative frequency (%) of management changes within each arm were compared using chi-square and Fisher's exact tests. KEY FINDINGS AND LIMITATIONS: The delivered SRT plan was available in 178/193 patients (92.2%;76/90 control [84.4%] and 102/103 PSMA-PET [99%]). Median prostate-specific antigen levels at enrollment was 0.30 ng/ml (interquartile range [IQR] 0.19-0.91) in the control arm and 0.23 ng/ml (IQR 0.15-0.54) in the PSMA-PET arm. Fluciclovine-PET was used in 33/76 (43%) in the control arm. PSMA-PET localized recurrence(s) in 38/102 (37%): nine of 102 (9%) outside of the pelvis (M1), 16/102 (16%) in the pelvic LNs (N1, with or without local recurrence), and 13/102 (13%) in the prostate fossa only. There was a 23% difference (95% confidence interval [CI] 9-35%, p = 0.002) of frequency of major changes between the control arm (22% [17/76]) and the PSMA-PET intervention arm (45%[46/102]). Of the major changes in the intervention group, 33/46 (72%) were deemed related to PSMA-PET. There was a 17.6% difference (95% CI 5.4-28.5%, p = 0.005) of treatment escalation frequency between the control arm (nine of 76 [12%]) and the intervention arm (30/102 [29%]). Treatment de-escalation occurred in the control and intervention arms in eight of 76 (10.5%) and 12/102 (11.8%) patients, and mixed changes in zero of 76 (0%) and four of 102 (3.9%) patients, respectively. CONCLUSIONS AND CLINICAL IMPLICATIONS: In this prospective randomized phase 3 study, PSMA-PET findings provided information that initiated major management changes to SRT planning in 33/102 (33%) patients. The final readout of the primary endpoint planned in 2025 may provide evidence on whether these changes result in improved outcomes. PATIENT SUMMARY: Prostate-specific membrane antigen positron emission tomography leads to management changes in one-third of patients receiving salvage radiotherapy for post-radical prostatectomy biochemical recurrence of prostate cancer.

Update from PSMA-SRT Trial NCT03582774: A Randomized Phase 3 Imaging Trial of Prostate-specific Membrane Antigen Positron Emission Tomography for Salvage Radiation Therapy for Prostate Cancer Recurrence Powered for Clinical Outcome.

The purpose of this randomized trial is to evaluate the success rate of salvage radiation therapy for recurrence of prostate cancer after radical prostatectomy, with and without planning based on prostate-specific membrane antigen positron emission tomography/computed tomography. Enrollment has been completed and patients are being followed for 5yr.