Single-Fraction Stereotactic Ablative Body Radiation Therapy As an Effective Management of Oligometastasis: Results from 133 Consecutive Patients

Patients with oligometastases are at significant risk of further distant recurrence despite local therapy. The primary objective of this study is to assess the freedom from widespread metastasis in patients with 1-3 oligometastases after receiving single fraction stereotactic ablative body radiation therapy (SABR). We defined widespread disease as distant recurrence not amenable to surgery or SABR; or development of ≥ 4 metastases. This retrospective review received institutional ethics approval for the study of patients treated with SABR for oligometastases between February 2010 and March 2015. These patients were followed up until September 2015. We included patients receiving single fraction SABR for 1-3 extracranial metastases. The prescription isodose coverage was typically to D99 with individual patient QA. Time to event outcomes were described using Kaplan-Meier methods with 95% confidence intervals. There were 187 treatments delivered in 133 patients during the study period. The median age of patients was 65. The most common primary malignancies were prostate cancer (n=34 patients), colorectal cancer (n=25), lung cancer (n=24) and bone and soft tissue sarcomas (n=15). The two main target sites treated were lung (51%) and bone (41%). The common prescription doses were 26 Gy /1# (47%), 20 Gy /1# (34%) and 24 Gy/1# (10%). The freedom from local progression at 1 year was 90% (95% CI 84% - 95%) and 2 years 84% (95% CI 76% - 92%). The freedom from distant progression was 52% at 1 year (95% CI 43% - 62%) and 39% at 2 years (95% CI 30% - 51%). The freedom from widespread disease was 74% at 1 year (95% CI 67% - 83%) and 60% at 2 years (95% CI 50% - 73%). The freedom from widespread disease after salvage SABR for further distant progression was 72% at 6 months (95% CI 60% - 88%) and 68% at 12 months (95% CI 54% - 86%). The 1 year overall survival was 99% (95% CI 97% - 100%) and 2 year overall survival was 87% (95% CI 79% - 97%). No Grade 3 or higher treatment related toxicity was reported, with 94 patients (50.8%) not suffering any toxicity. Single fraction SABR is associated with a high rate of freedom from widespread disease, excellent local control, favorable overall survival, and low toxicity profile. Single fraction SABR is a resource efficient treatment that may delay the need for active systemic treatment in patients with oligometastatic disease.