1567. Evaluating Kyphosis with and without Stabilization Surgery Using Multifraction Stereotactic Body Radiation Therapy for Spine Metastases

Authors: Krisztina Moldovan, MD; Jonathan Nakhla, MD; Yaroslav Gelfand, MD; Rafael De La Garza Ramos, MD; Sean Barber, MD; Sanjay Konakondla, MD; Jared Fridley, MD; Albert Telfeian, MD, PhD; Ziya Gokaslan, MD; Jaroslaw Hepel, MD; Adetokunbo Oyelese, MD, PhD (Providence, RI)

Introduction: Kyphosis is a known complication of pathological fractures treated with multifraction stereotactic body radiation therapy (SBRT). Single-fraction radiation surgery for spine metastases is highly effective; however, the outcomes and long-term complication of kyphosis has not been evaluated. Methods: All patients who were treated with SBRT for spine metastases at our institution between 2009 and 2017 were retrospectively analyzed. SBRT was delivered in 2 to 5 fractions using the Cyberknife System. Two groups of lesions were analyzed: the ones who underwent stabilization surgery, and the ones that did not undergo stabilization. Patients were followed clinically and with MRI every 3 to 6 months. Vertebral body fractures (VBF) and kyphosis were evaluated and univariate analysis was used to assess the relationship between development of kyphosis at the treatment level and stabilization procedures. Results: A total of 98 spine lesions in 89 patients were reviewed with a median follow-up of 7.6 months. Histologies included non-small cell lung cancer (24%), renal cell carcinoma (18%), and breast cancer (12%). Surgery or vertebroplasty were performed before SBRT in 21% of cases. Higher prescribed dose, higher biologic effective dose, higher minimum dose to 90% of the planning target volume, tumor histology, and smaller tumor volume predicted improved local control. VBF occurred in 4.2% of all cases and 5.3% of those without surgery or vertebroplasty prior to SBRT. Only preexisting VBF predicted risk of post-SBRT VBF (P < .01). Out of 90 lesions that were not subject to stabilization 12 (13.3%) developed kyphosis, as compared to 0 out of 8 lesions in the stabilization group. Conclusion: Although the statistical significance was not reached comparing kyphosis in stabilization and non-stabilization groups (p=0.270), we propose that since none of the lesions in the stabilization group resulted in kyphosis, stabilization surgery is superior in preventing kyphotic deformity in SBRT.