Utilization of stereotactic ablative radiotherapy in oligometastatic & oligoprogressive skeletal metastases: Results and pattern of failure.

AIM: To evaluate the outcome and toxicities of stereotactic ablative radiotherapy (SABR) for skeletal metastasis in a tertiary cancer center. METHODS: This is a retrospective review of 22 patients treated with SABR for skeletal metastases for oligometastases (OM) or oligoprogression (OP) since October 2012. There are a total of 27 treatments with 20 spinal and seven non-spinal metastases. Treatment outcome including local control (LC), progression-free survival (PFS), overall survival (OS), pain control, treatment-related toxicity and failure pattern are described. Patients are assessed by interval computed tomography (CT), positron emission tomography-CT, magnetic resonance imaging or bone scintigraphy by physicians' discretion. Toxicities are graded by common toxicities criteria version 4.03. RESULT: The median age of the patients is 64 years. Primary sites include lung (50%), breast (32%), nasopharynx (9%), prostate (4.5%) and colon (4.5%). Twelve patients with OM and 10 with OP are included. Dose to most spinal and non-spinal metastases is 35 and 50 Gy, respectively, in five fractions. With a median follow up of 15.6 months, there are three local failures (1-year LC 91.2%). The median PFS and OS are 10.1 and 37.3 months, while PFS of OP and OM group is 6.6 and 10.6 months, respectively. Two-third of symptomatic patients have at least 1-year complete pain control. There are two vertebral fractures and one grade 3 esophagitis. CONCLUSION: Our series shows excellent LC of SABR to skeletal metastases with limited toxicities in OM and OP diseases. However, its benefit of survival warrants further studies.