Reirradiation With Stereotactic Body Radiation Therapy for Spinal Metastases: Planning Procedure From a High-Volume Multidisciplinary Spine Oncology Program (SOaR2)

We sought to develop a systematic spine reirradiation planning protocol prioritizing patient safety and maximizing tumor dose delivery. Patients were presented at a Multidisciplinary Spine Oncology Tumor Board to confirm suspicion for recurrent or progressive malignancy and were evaluated in the clinic by the Department of Radiation Oncology and Neurosurgery. Suitable patients proceeded to computed tomography (CT)/magnetic resonance imaging scan simulation. A dedicated physics pathway was activated with the fusion of the magnetic resonance imaging scan and planned CT scan, verified independently by 2 physicists. The prior radiation data set was registered to the new imaging data set, and the prior dose was displayed on the new imaging data set. Physical dose, equivalent dose in 2 Gy fractions (EQD₂) α/β = 2, and EQD₂ α/β = 3 plans were generated to evaluate prior dose to organs at risk (OARs). Target volumes were defined on the new data set. Dose, fractionation, and OAR constraints were prescribed by the treating physician in accordance with the literature, with priority given to respecting OARs. The constraints were stipulated as EQD₂-based objectives and converted to physical doses for the current plan. A plan-sum of the current course and all prior courses was created and displayed on the new imaging data set for evaluation. Composite, EQD₂ α/β = 2, and EQD₂ α/β = 3 plans were generated to evaluate current and cumulative dose to the target and OARs. Treatment was delivered on a 6°-of-freedom couch with pretreatment, midtreatment, and posttreatment cone beam CT scan imaging. Registration-based shifts > 2 mm or 1° were evaluated. When requested, physicists performed quantitative analysis of dosimetric impact using a forward calculation of the plan on the planning image with the treatment shifts applied to determine whether an offline plan adaptation is necessary. Our protocol contributed to the growing literature on spinal reirradiation with stereotactic body radiation therapy and enabled safe treatment in cases of incidental spinal cord exposure. We developed a systematic approach to planning and delivering spinal reirradiation with stereotactic body radiation therapy.