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 spine stereotactic radiosurgery (SSRS), allowing for spinal cord dose constraint relaxation, as the primary management of metastatic epidural spinal cord compression (MESCC) in inoperable patients. Inoperable patients with thoracic MESCC and no history of radiation were enrolled on this prospective phase 1 single-institution protocol. SSRS was delivered to a histology-dependent prescription dose of 18 or 24Gy. Incremental spinal cord constraint relaxation was performed from a Dmax cohort of 10Gy up to 16Gy only if tumor progression occurred and the risk of radiation-induced myelopathy (RM) remained lower than the risk of tumor progression. Thirty-two patients enrolled on the trial; 4, 12, 9, and 7 patients were in the 10Gy, 12Gy, 14Gy, and 16Gy cord Dmax cohorts, respectively. At baseline, there were 2 sites with MESCC grade 1A, 10 sites with grade 1B, 10 sites with grade 1C, 9 sites with grade 2, and 1 site with grade 3 disease. Among the 28 evaluable patients, the median overall survival was 28.6months (95% confidence interval [CI], 9.2-48.0months), and the 1-year local control was 89% (95% CI, 74%- 97%). With a median follow-up of 17months, there were no cases of RM (upper 95% CI, 12%). In the cohort receiving a cord Dmax of 16Gy, there were no cases of RM (upper 95% CI, 39%) with a median follow-up of 17months (range, 12.7-21.0months). SSRS is a safe and effective tool in patients with MESCC. In high-risk inoperable patients with MESCC receiving SSRS, dose constraint relaxation of the cord constraint dmax to 16Gy may be considered to optimize local control, with the acknowledgment that this is based on 6 evaluable patients who received this dose in this trial.