Radiation Dose To Ipsilateral Subventricular Zone As A Prognostic Factor In Malignant Glioma Patients

ranging from 18-30 Gy in 1-6 fractions (54% were 24 Gy x 1). All patients were evaluated and managed by a multidisciplinary spine team including a radiation oncologist, neurosurgeon, and interventional radiologist. Twentyseven percent of lesions were surgically resected prior to SBRT and 48% of lesions had radiographic epidural disease at time of SBRT. All sites of progression within the spinal axis were mapped according to number of vertebral levels away from the treated lesion. Kaplan-Meier method was used to capture actuarial rates, and R-squared statistics were used to assess correlation. Results: The median follow-up for the cohort was 14.4 months, with 82% of patients followed until death. At the time of last follow-up, 47% (nZ56) of patients had not progressed at any site in the spinal axis. Of the remaining 53% (nZ64), only 23% (nZ15) progressed at a single vertebral level, with 59% (nZ38) progressing at 3 sites within the spine simultaneously. The 1-year actuarial local failure-free survival (LFFS), adjacent segment failure-free survival (ASFFS), and distant segment failure-free survival rates were 87%, 85%, and 66%, respectively. However, 75% of local failures and 90% of adjacent segment failures occurred in conjunction with distant spine failures. The 1-year actuarial rate for isolated LFFS and isolated ASFFS were 96% and 98%, respectively. The patterns of failure by distance from the treated lesion were 8.4% crude failure at the index lesion and 10.8%, 11.6%, 10.3%, and 6.8% for lesions 1, 2, 3, and 4 segments away. Linear regression analysis revealed a relationship of decreasing risk of failure with increasing distance from the treated index lesion (R Z 0.87), and 52% occurred 5 segments away. Conclusion: We report the first detailed spinal axis patterns of failure analysis for patients undergoing SBRT for metastatic osseous spine disease. We demonstrate that local control is excellent, and importantly, isolated local and adjacent segment failures are 5 vertebral levels away from the index lesion. Thus, total spine imaging in close interval is requisite for surveillance post-treatment. Author Disclosure: J.E. Leeman: None. M. Bilsky: None. I. Laufer: None. M.R. Folkert: None. N.K. Taunk: None. J.R. Osborne: None. J. Zatcky: None. K.M. Alektiar: None. Y. Yamada: Consultant; Varian Medical. D.E. Spratt: None.