Long-term Results From a phase 1 Study of Spinal Cord Constraint Relaxation With Single Session Spine Stereotactic Radiosurgery in the Primary Management of Patients With Inoperable, Previously Unirradiated Spinal Metastases With Epidural Extension.

Purpose: We seek to report long-term results of a phase 1 protocol relaxing the spinal cord dose constraint when using spine stereotactic radiosurgery (SSRS) in the primary management of spinal metastases with epidural extension in inoperable patients.

Methods And Materials: Inoperable patients with previously unirradiated thoracic metastatic epidural spinal cord compression (MESCC), ranging from impending cord compression to true cord compression, received single-fraction SSRS on this phase 1 protocol. Incremental spinal cord constraint relaxation was performed from an initial allowable maximum dose delivered to 0.01 cm of the spinal cord (Dmax) cohort of 10 Gy up to 16 Gy.

Results: Thirty-two patients enrolled in the trial, of which 4, 12, 8, and 8 were in the 10, 12, 14, and 16 Gy cord Dmax cohorts, respectively. The median age was 62.7 years. 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 disease. Of the 28 evaluable patients, the median overall survival of the cohort was 28.6 months (95% CI, 19.4-76.3 months). The 1- and 2-year local control (LC) was 85% (95% CI, 72%-100%) and 80% (95% CI, 65%-98%), respectively. Within the high-cord Dmax cohorts (14 and 16 Gy), the 2-year and 5-year LC was 93% (95% CI, 80%-100%) compared with 63% for the low-cord Dmax cohort (95% CI, 39%-100%). With a median clinical follow-up of 22 months (range, 3.4-141.3 months), there were no cases of RM (95% CI, 0%-12.3%).

Conclusions: With long-term follow-up, SSRS is a safe and effective tool in patients with spinal metastases with epidural extension. The high-cord Dmax cohort demonstrated 2- and 5-year LC of 93% compared with 63% in the low-cord Dmax cohort. Cord constraint relaxation may be considered in inoperable patients with MESCC.