Three-year update of outcomes for SABR-treated extracranial oligometastases: A real world experience

Abstract

Purpose or Objective We present real-world data from a single institution demonstrating longer term treatment outcomes in patients who have received SABR for oligometastases in addition to standard of care management. We compared our treatment outcomes and safety and safety against published data. Materials and Methods We retrospectively collated 5-year outcomes for patients with oligomatastases treated with SABR from February 2016 to September 2021. Inclusion criteria were as per the UK SABR Consortium Guidelines1. Prescribed doses ranged between 25- 60Gy in 3-8 alternate day fractions. The primary endpoints were: local in-field control rate (LC), distant relapse (DR) for Years 1, 2 and 3, median overall survival (OS), progression free survival (PFS) and median time to further subsequent treatment (TFST). Tumour biologically effective dose (BED) was calculated using α/β ratio of 10. When applicable, endpoints were estimated from SABR treatment end date. Toxicity data (≥ G3) was collected and assessed using CTCAE v5.0. Results A total of 142 patients received 152 treatments (10 patients had SABR for 2 sites). Patients’ characteristics are shown in table-1. Mean tumour BED was 96.4 Gy (range 43.2-180) for the prescribed doses. Median follow up was 33 months (range 0-65), Median LC for years 1, 2 and 3 was 89.4%, 83.5% and 82.2% respectively. OS for years 1, 2 and 3 was: 89.1%, 77.8% and 72.4% respectively. Median OS is not yet reached (Fig-1). DR was 66.4%, 52.6% and 47.3% for years 1, 2 and 3 respectively. Median times to: local in-field recurrence (LR) and DR were 10 and 9 months respectively. Median local and distant PFS was 19 months. Median TFST was 12 months (range 0-36). G3 toxicities observed in 1.4% (2/142) (spinal fracture and fatigue). No ≥G4 toxicities. Conclusion Our cohort showed that SABR for oligometastases offers high rates of local control with minimal toxicity. Our outcomes for LC, OS and PFS are consistent with the UK NHS CtE registry study2 and SABR COMET3. In our series, we have shown that SABR delayed subsequent treatment by a median of 12 months. Ongoing trial results are awaited to further determine the benefit of adding SABR to the standard-of-care therapy for oligometastases.