Long-term outcomes of SBRT for PSMA PET detected oligometastatic prostate cancer

Abstract

Purpose: Managing oligometastatic disease recurrence in prostate cancer patients is a challenging clinical scenario seen frequently with the widespread utilisation of PSMA-PET scans which have resulted in the earlier detection and delineation of oligometastatic disease. Whilst many clinicians may recommend systemic therapy, the option of focal SBRT aims to defer androgen deprivation and may deliver sustained biochemical failure free survival. However, minimal long-term data is available on the effectiveness of such an approach.

Methods and Materials: This is retrospective cohort of patients who received PSMA-PET directed SBRT without ADT for oligo-metachronous prostate cancer. The primary endpoint was time to biochemical failure defined as PSA rising 0.2ng/ml above nadir. Secondary endpoints were time to ADT, a priori PSA nadir +2 ng/ml, failure free survival, toxicity, patterns of failure and survival. Patients were excluded if they had supressed testosterone at the time of SBRT or if they received any ADT with SBRT.

Results: 103 patients were analysed, with a median follow up of 4.9 years. 63 patients were treated for nodal oligometastatic disease only, 56 of these were confined to the pelvis. Median time to biochemical failure (nadir + 0.2ng/ml) was 1.1 years, with a 5-year biochemical failure free survival of 19%. No predictive features for biochemical failure free survival were identified. A total of 33 patients had further definitive radiation therapy following biochemical failure of initial SBRT, including subsequent SBRT or pelvic nodal/prostate bed radiation with 12 of these biochemically disease free at last follow up. Median time to ADT for the entire cohort was 5.5 years with 55% free of ADT at 5 years. There were no grade 3 or 4 toxicities. No local failures were identified.

Conclusion: PSMA PET guided SBRT for oligo-metachronous prostate cancer recurrence results in excellent local control and low toxicity and serves as an effective strategy for ADT avoidance with nearly 1 in 5 patients attaining prolonged biochemical failure free survival. Further large randomised prospective studies with long term follow up are required.