Stereotactic radiotherapy for spinal hemangioblastoma - disease control and volume analysis in long-term follow up.

Background: This retrospective analysis evaluated the long-term outcome of spinal stereotactic body radiotherapy (SBRT) treatment for hemangioblastomas. Materials and methods: Between 2010 and 2018, 5 patients with 18 Von-Hippel Lindau-related pial-based spinal hemangioblastomas were treated with fractionated SBRT. After precisely registering images of all relevant datasets, we delineated the gross tumor volume, spinal cord (including intramedullary cysts and/or syrinxes), and past radiotherapy regions. A sequential optimization algorithm was used for dose determinations, and patients received 25-26 Gy in five fractions or 24 Gy in three fractions. On-line image guidance, based on spinal bone structures, and two orthogonal radiographs were provided. The actuarial nidus control, surgery-free survival, cyst/syrinx changes, and progression-free survival were calculated with the Kaplan-Meier method. Toxicities were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events v5.0. Results: The median follow-up was 5 years after SBRT. Patients displayed one nidus progression, one need of neurosurgery, and two cyst/syrinx progressions directly connected to symptom worsening. No SBRT-related complications or acute adverse radiation-related events occurred. However, one asymptomatic radiological sign of myelopathy occurred two years after SBRT. All tumors regressed; the one-year equivalent tumor volume reduction was 0.2 mL and the median volume significantly decreased by 28% (p = 0.012). Tumor volume reductions were not correlated with the mean (p = 0.19) or maximum (p = 0.16) dose. Conclusions: SBRT for pial-based spinal hemangioblastomas was an effective, safe, viable alternative to neurosurgery in asymptomatic patients. Escalating doses above the conventional dose-volume limits of spinal cord tolerance showed no additional benefit.