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.