Stereotactic ablative body radiotherapy for PSMA-PET/CT staged, oligometastatic prostate cancer - A multi-centre study.

[BACKGROUND AND PURPOSE] Stereotactic ablative body radiotherapy (SABR) for oligometastatic prostate cancer (omPC) has proven a topic of emerging interest in the paradigm shift from palliative androgen deprivation therapy (ADT) to metastasis-directed therapy. In this study, we aim to evaluate and report on biochemical and clinical outcomes for omPC patients treated with SABR.

[METHODS AND MATERIALS] This was a multi-centre, retrospective case series of patients undergoing SABR for omPC from 2015 to 2019 inclusive, staged with PSMA-PET/CT. Concurrent ADT was permitted. Patients with synchronous metastatic disease receiving radiotherapy to primary within 12 months of SABR were excluded. The primary endpoint was biochemical failure-free survival (BCFFS). Secondary endpoints included: PSA response at 6 months, clinical failure-free survival (CFFS), defined by a 2nd course of SABR, commencing ADT, palliative radiotherapy, systemic therapy or changing current line of therapy; ADT-free survival (FS) was calculated in the SABR only cohort.

[RESULTS] 213 patients were included for analysis. 41.3 % of SABR was delivered to bone and 49.3 % to nodal metastases, with 28 patients (13.1 %) having SABR together with ADT. Median follow-up was 57.6 months (IQR 45.8-72.6). BCFFS at 12, 24 and 36 months was: 45.6 % (95 %CI: 38.7-52.2 %), 26.2 % (95 %CI: 20.4-32.4 %) and 18.8 % (95 %CI: 13.7-24.5 %), respectively. CFFS at 12, 24 and 36 months was: 71.4 % (95 %CI: 64.7-77.0 %), 50.4 % (95 %CI: 43.4-57.1 %) and 39.2 % (95 %CI: 32.4-45.8 %), respectively.Median ADT-FS was 41.98 months (95 %CI: 32.76-52.90), with 5-year ADT-FS reported at 37.5 % (95 %CI:29.8-45.1 %).

[CONCLUSION] This is the largest cohort of PSMA PET staged patients undergoing SABR for omPC, effective in delaying treatment escalation and ADT exposure beyond 3 years.