Outcomes After Hypofractionated Dose-Escalation using a Simultaneous Integrated Boost Technique for Treatment of Spine Metastases Not Amenable to Stereotactic Radiosurgery

Purpose: Spine stereotactic radiosurgery delivers an ablative dose of radiation therapy (RT) with high conformity relative to standard fractionated RT. This technique is suboptimal for extended targets (>3 vertebral levels) owing to treatment alignment concerns or for patients with marked epidural extension. In these patients, we hypothesized that use of hypofractionated intensity modulated RT/volumetric modulated arc therapy to dose escalate the gross tumor volume (GTV) to 40 Gy as a spinal simultaneous integrated boost (SSIB) would allow for durable local control and palliation. Methods and Materials: We retrospectively analyzed 15 separate spinal sites (12 patients) that were treated with the SSIB technique between 2012 and 2016. The GTV and clinical target volume were prescribed at 40 Gy and 30 Gy, respectively, in 10 fractions. The spinal cord was allowed a maximum point dose of 34 Gy. The GTV was defined as gross tumor. The clinical target volume encompassed the GTV in addition to the involved vertebral bodies, at-risk paraspinal space, and spinal canal, followed by a planning target volume expansion of 3 to 5 mm. Results: The median follow-up for patients in our cohort was 17 months. At 1 year, local control was 93%, and overall survival was 58%, with a median time to death after treatment of 7 months. No grade ≥2 neurologic toxicities were reported for any of the patients. Nine of 12 patients had pain at presentation, of which 7 patients (78%) reported improvement and/or complete resolution of their pain after treatment. Conclusions: Our early experience using a dose of 40 Gy to the GTV delivered via an SSIB technique, in lieu of spine stereotactic radiation surgery but more aggressive than conventional palliative doses, provides durable local control and pain relief. This technique may allow for improved local control and palliation in patients with radioresistant disease compared with conventional 3-dimensional conformal fractionated RT.