Stereotactic Ablative Body Radiotherapy for the Treatment of Spinal Oligometastases

Abstract

Aims: To report multicentre outcomes of patients with spinal oligometastases treated with stereotactic ablative body radiotherapy (SABR). The primary objective was to estimate the widespread failure-free survival (WFFS) at 2 years - defined as freedom from metastases not amenable to local salvage therapy and death.

Materials and methods: Patients with one to three metastases treated with spinal SABR between January 2010 and July 2014 at four academic institutions were included in this retrospective review. The median dose/fractionation was 24 Gy (range 16-52.5 Gy) in two fractions (range one to three) and the median biologically effective dose (α/β=10) was 52.5 Gy (range 40-144.4 Gy). The WFFS, overall survival, freedom from local progression and toxicity rates were described using Kaplan-Meier statistics.

Results: In total, 60 patients with 72 spinal metastases were analysed. The median follow-up was 21 months. Patients had a median age of 66 years, Eastern Cooperative Oncology Group performance 0-1 in 97% and metachronous oligometastases in 85%. The 1 and 2 year WFFS rates were 67% (95% confidence interval 55-80) and 59% (95% confidence interval 47-75), respectively. The 1 and 2 year overall survival rates were 90% (95% confidence interval 83-98) and 76% (95% confidence interval 64-91), respectively. The 1 and 2 year freedom from local progression were 92% (95% confidence interval 85-99) and 86% (95% confidence interval 75-99), respectively. There were four cases (6.7%) of vertebral compression fracture and no cases of radiation myelopathy.

Conclusion: Despite the use of relatively low biological doses respecting spinal cord constraints, SABR results in excellent 2 year local control rates with low morbidity. Through careful selection of patients with oligometastases, most patients are alive and free from widespread metastases at 2 years. This cohort warrants further investigation in clinical trials of SABR.

Keywords: Intensity-modulated radiotherapy; metastasis; radiosurgery; spine; stereotactic body radiotherapy.