Stereotactic Proton Ablative Radiosurgery of the Spine

Abstract

To report the techniques of treating primary tumors and metastases of the spine with stereotactic proton ablative radiotherapy.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.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.Stereotactic proton ablative radiotherapy for the treatment of tumors and metastases of the spine is a safe and effective treatment modality.M. Dougherty: None. T.C. Mullikin: None. S.S. Park: None.