Volumetric Intensity-Modulated Arc Stereotactic Radiosurgery Boost in Oligometastatic Patients with Spine Metastases: a Dose-escalation Study

Aims: To report the final results of a dose-escalation study of volumetric intensity-modulated arc stereotactic radiosurgery (VMAT-SRS) boost after three-dimensional conformal radiation therapy in patients with spine metastases. Materials and methods: Oligometastatic cancer patients bearing up to five synchronous metastases (visceral or bone, including vertebral ones) and candidates for surgery or radiosurgery were considered for inclusion. 25 Gy was delivered in 10 daily fractions (2 weeks) to the metastatic lesion, affected vertebrae and adjacent ones (one cranial and one caudal vertebra). Sequentially, the dose to spinal metastases was progressively increased (8 Gy, 10 Gy, 12 Gy) in the patient cohorts. Dose-limiting toxicities were defined as any treatment-related non-hematologic acute adverse effects rated as grade ≥3 or any acute haematological toxicity rated as ≥ 4 by the Radiation Therapy Oncology Group scale. Results: Fifty-two lesions accounting for 40 consecutive patients (male/female: 29/11; median age: 71 years; range 40–85) were treated from April 2011 to September 2020. Most patients had a primary prostate (65.0%) or breast cancer (22.5%). Thirty-two patients received 8 Gy VMAT-SRS boost (total BED α/β10: 45.6 Gy), 14 patients received 10 Gy (total BED α/β10: 51.2 Gy) and six patients received 12 Gy (total BED α/β10: 57.6 Gy). The median follow-up time was over 70 months (range 2–240 months). No acute toxicities > grade 2 and no late toxicities > grade 1 were recorded. The overall response rate based on computed tomography/positron emission tomography–computed tomography/magnetic resonance was 78.8%. The 24-month actuarial local control, distant metastases-free survival and overall survival rates were 88.5%, 27.1% and 90.3%, respectively. Conclusion: A 12 Gy spine metastasis SRS boost following 25 Gy to the affected and adjacent vertebrae was feasible with an excellent local control rate and toxicity profile