Stereotactic Proton Ablative Radiosurgery of the Spine.

PURPOSE/OBJECTIVE(S): To report the techniques of treating primary tumors and metastases of the spine with stereotactic proton ablative radiotherapy.

MATERIALS/METHODS: Robustly optimized IMPT plans were generated using either the Single-field optimization (SFO) or the multi-field optimization (MFO) method in the treatment planning system. Patients with primary and metastatic lesions of the spine, who underwent curative-intent, received ablative pencil-beam scanning proton therapy between July 2015 and October 2019. Patients were immobilized with thermoplastic mask or vac lok, indexed knee cushion, and memory foam. Radiotherapy was delivered CT-on-Rail image guidance. MRI, CT, and/or PET-CT were assessed for radiographic local control. Outcomes were measured from radiation end date to last imaging. Acute and long-term adverse events (AE) were assessed based on CTCAE v4.0.

RESULTS: Forty-four patients were identified. Forty-nine unique metastatic spine sites were treated, C-spine (n = 2), T-spine (13), L-spine (18), and sacrum (16). The median age was 64. 44% were prostate histology. 80% had prior overlapping radiotherapy fields, and 20% were retreatment. The median dose per fraction and number of fractions were 13 Gy (R, 10-22 Gy) and 3 (R, 1-5). The Median follow-up was 22.2 months. Overall survival at 1 and 2 years was 79.1% and 73.8%. Forty-five patients were surveilled with imaging. The radiographic local control at 1 and 2 years was 74.0% and 56.2%. Local failure-free survival at 1 and 2 years was 60.6% and 40.9%. All patients were assessed during and following radiotherapy for acute and long-term toxicities. Acutely, 9 (18%) patients experienced a pain flare with 4, requiring initiation or increased opioids or steroids for pain management. Three patients experienced acute grade 1 peripheral sensory neuropathy, and one patient, acute grade 1 esophagitis. Long term, there was one de novo vertebral body compression fracture requiring vertebroplasty and three patients with grade 1-2 sensory peripheral neuropathy.

CONCLUSION: Stereotactic proton ablative radiotherapy for the treatment of tumors and metastases of the spine is a safe and effective treatment modality.

AUTHOR DISCLOSURE: M. Dougherty: None. T.C. Mullikin: None. S.S. Park: None.