Oligometastatic Disease State Is Associated with Improved Local Control in Patients Undergoing Three or Five Fraction Spine Stereotactic Body Radiotherapy.

Background: The objective of our study was to describe the local control (LC) outcomes with 3- or 5-fraction stereotactic body radiotherapy (SBRT) to the spine in patients with oligometastatic (≤5 systemic metastases) versus polymetastatic disease (>5 metastases).

Methods: We retrospectively reviewed the outcomes of patients who had undergone SBRT for spinal metastases. No patients had undergone previous surgical intervention or had spinal cord compression. All patients were treated with 3-fraction (median dose, 27 Gy; range, 24-30 Gy) or 5-fraction (median dose, 35 Gy; range, 25-40 Gy) SBRT. The Kaplan-Meier method and Spine Response Assessment in Neuro-Oncology criteria were used to determine LC.

Results: We included 61 patients with a total of 72 distinct SBRT targets who had been treated from August 2007 to June 2017. The median follow-up period was 13.58 months. We treated 20 targets and 52 targets with 3 and 5 fractions, respectively. Thirteen patients (18.1%) had undergone previous RT to the SBRT area. Twenty patients (35% of the distinct SBRT targets) had an oligometastatic disease state. The 1-year LC rate was 83% for the entire cohort. On univariable analysis, polymetastases (1-year LC, 73.8% vs. 100%; P = 0.07) showed a trend toward worse LC. On multivariable analysis, patients with an oligometastatic state (hazard ratio, 0.21; P = 0.04) had improved LC.

Conclusions: Our study was hypothesis-generating in that patients with an oligometastatic disease state appear to have improved LC after SBRT, suggesting a biological advantage exists with local therapy for this group of patients not seen for patients with polymetastatic disease.