Long Term Outcomes after Re-Irradiation With Spine Stereotactic Body Radiation Therapy: Single Institutional Retrospective Experience

Re-irradiation of spinal metastases using stereotactic body radiotherapy (SBRT) presents clinical challenges, with limited patient outcomes data to guide decision-making. We report a retrospective, single-institutional experience of 107 lesions treated in 91 patients. 88 (72%) lesions were initially irradiated with conventional radiotherapy (median equivalent dose of 33Gy to the target, interquartile range, IQR: 23-35 Gy) with a median time to re-irradiation of 12 months (IQR: 4-21 months). For re-irradiation, most lesions received either 1 fraction (18-24 Gy) or 3 fractions (30-36 Gy) of SBRT. The median equivalent dose in 2Gy fractions was 38 Gy (IQR: 30-41 Gy), 27 Gy (22-36 Gy), and 65 (54-73Gy) for previous courses, re-irradiation, and cumulatively, respectively. At one year, overall survival was 61% with a cumulative incidence of local failure at 12% and vertebral compression fracture at 9% considering death as a competing risk. None of the 79 treated lesions at L1 or above developed radiation myelitis, but 5 patients developed chronic peripheral neuropathy. In our analysis, most adverse events or local failures occur within the two years after retreatment. These findings demonstrate the safety and effectiveness of spine reirradiation with SBRT.