Phase 1 Study of Spinal Cord Constraint Relaxation with Single Session Spine Stereotactic Radiosurgery in the Primary Management of Patients with Inoperable, Previously Unirradiated Metastatic Epidural Spinal Cord Compression

Abstract

We seek to establish the feasibility of using SSRS allowing for spinal cord dose constraint relaxation as the primary management of MESCC in inoperable patients monitoring for radiation related toxicity and radiographic local control (LC). Patients with MESCC in the thoracic spine deemed inoperable with no prior history of radiation at the site of interest were enrolled on this prospective Phase 1 single institution protocol. Single fraction SSRS was delivered to a histology dependent prescription dose of 18 or 24 Gy. Spinal cord constraint relaxation was performed from an initial allowable Dmax cohort of 10 Gy only if tumor progression occurred. If the risk of radiation induced spinal cord myelopathy (RM) remained lower than the risk of tumor progression, then the cord Dmax was elevated in 2 Gy increments to a maximum of 16 Gy in the final cohort. Patients were monitored every 3 months with follow-up visits, MRI scans and validated patient reported outcome surveys. Thirty-two patients enrolled on the trial of which 4, 12, 8, and 8 were in the 10 Gy, 12 Gy, 14 Gy, and 16 Gy cord Dmax cohorts, respectively. The most common histology was renal cell carcinoma (n = 12). The most common GTV prescription dose was 18 Gy (n = 17) followed by 24 Gy (n = 15). The median age was 62.7 yrs (range 35-81 yrs). At baseline, there were 10 sites with MESCC Grade 1B, 10 sites with Grade 1C, 9 sites with Grade 2, 2 sites with Grade 1A, and 1 site with Grade 3 epidural extension of disease. The median overall survival of the cohort was 28.6 mos (95% CI 19.6, NR). Of the 32 patients treated with SSRS, 4 were lost to follow-up without post-SSRS evaluation. Of the remaining 28 patients, the 1-year LC was 80.5% and median LC was not met. With a median clinical follow-up of 17.2 months (range 3-35.7 mo), there were no cases of RM. In the cohort receiving a cord Dmax of 16 Gy, there were no cases of RM with a median follow-up of 15.4 mo (range 6.4-21.0 mo). SSRS is a safe and effective tool in patients with MESCC. Cord constraint relaxation may be considered in inoperable patients with MESCC.