Fractionated Spine Stereotactic Body Radiotherapy for Treatment of Primary and Metastatic Sarcoma

Abstract

Sarcomas are biologically characterized by aggressive local spread and a relative insensitivity to radiotherapy. Our group previously reported that single fraction spine stereotactic radiosurgery (sSRS) for sarcomas was associated with suboptimal local control. This study analyzes whether fractionated sSRS is associated with improved radiographic control and reduced risk for pain flare as compared to single fraction sSRS. We conducted a retrospective review of patients with metastatic or primary spine sarcoma treated with sSRS at a single tertiary care institution over a decade. Patient, treatment and dosimetric variables and clinical outcomes were retrospectively reviewed using an IRB-approved prospective database. Rates of radiographic failure and pain flare were compared with the chi squared test. A total of 76 patients underwent sSRS for primary or metastatic sarcoma between 2006 and 2016 with a mean follow up was 16 months. Of these, 18 patients were treated with fractionated sSRS. Patients treated with fractionated sSRS tended to be younger (42.4±22.9 vs. 53.9±14.3; p=0.01), have a lower KPS (71.8±12.4 vs. 80.2±11.5; p=0.01), and were more likely to have oligometastatic disease (77.8% vs. 44.8%; p=0.05). All other patient characteristics were similar. Patients treated with single fraction sSRS received an average dose of 15Gy (range 10-18Gy). Patients treated with fractionated sSRS received a mean dose of 30 Gy (range, 24-40 Gy) in 3-5 fractions. In single fraction patients 24/58 (41.4%) experienced radiographic progression as compared to 4/18 (22.2%) in fractionated sSRS patients (p=0.14). Univariable competing risk regression with death as a competing risk showed that fractionated sSRS was associated with a decreased risk of radiographic progression (HR=0.52, 0.17-1.59; p=0.25), although this finding was not significant. Additionally, in single fraction patients, 10/58 (17.2%) experienced pain flare as compared to 1/18 (5.6%) in fractionated sSRS patients (p=0.22). Similarly, univariable competing risks analysis showed that fractionated sSRS was associated with a decreased risk of pain flare (HR=0.30, 0.04-2.15; p=0.23), although this was not statistically significant. Treatment of primary and metastatic sarcoma with sSRS has demonstrated a trend towards superior radiographic control and decreased pain flares. In our experience from a small sample, we have seen a two-fold decrease in radiographic failure and three-fold decrease in pain flare among patients treated with fractionated sSRS. Although patients treated with fractionated sSRS tended to be younger, they had a lower functional status and were more likely to have oligometastatic disease. Further research with larger sample sizes is warranted to establish the role of fractionated sSRS in this population.