2510 - Dosimetric Analysis of Salvage SBRT Reirradiation after Initial Spine SBRT; Single Institution Experience

A. N. Elguindy^1,2, R. Handschuh¹, K. Dibs¹, W. Zoller¹, M. Addington¹, D. Eiler¹, K. Fernando³, E. Cochran¹, D. J. DiCostanzo¹, J. B. Elder⁴, V. Chakravarthy⁴, R. Raval¹, E. M. Thomas¹, S. Beyer¹, A. Chakravarti¹, J. D. Palmer¹, and D. Blakaj¹; ¹Department of Radiation Oncology, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH, ²Ain Shams university hospital, Cairo, Egypt, ³department of radiation oncology, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH, ⁴Department of neurosurgery, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH

Purpose/Objective(s): Spine stereotactic radiation therapy (SRT) shows superior pain and local control for spine metastatic lesions compared to conventional radiation. Despite this, challenges exist to retreat recurrent cases. The purpose of this study is to share our experience on spine metastases patients who received salvage SRT after initial SRT. Materials/

Methods: A retrospective analysis of locally recurrent metastatic spine disease treated between 2016-2023 with salvage spine re-SRT. Follow up MRI was obtained every 3months after the re-SRT. Response was assessed with the SPIne response assessment in Neuro-Oncology (SPINO) group report. Radiation toxicity was graded based on the Common terminology criteria for adverse events (CTCAE) v5.0. Primary endpoint was radiation toxicity and local control after the re-SRT. Dose data from each treatment for spinal cord (SC), SC + 2mm, cauda equina (CE), CE + 2mm, and thecal sac (TS) were used to calculate biological effective dose (BED) using alpha/beta= 2Gy for cervical/thoracic spine and alpha/beta= 4Gy for lumbar/sacral spine.
Results: Twenty-two patients were treated with SRT twice to the same spine metastases, 95% (21/22) of pts were ECOG 0-1, 63.5% (14/22) had cervicothoracic metastasis and 36.5% (8/22) had lumbosacral spine metastasis. Histopathology was lung cancer (32%), RCC (18%), Colon cancer (13.5%), soft tissue sarcoma (13.5%), and paraganglioma (9%). Bilsky grading, 63.5% (14/22) with grade 0- 1b, 18% (4/22) with 1c, 9% (2/22) with 2, and 4.5% (1/22) with 3. SINS scores are 63.5% (14/22) stable and 36.5% (8/22) intermediate. Nine cases (41%) had spine surgery after initial SRT. 2 weeks around re-SRT, 45.5% (10/22) received tyrosine kinase inhibitors and 18% (4/22) received immunotherapy. All patients had follow-up imaging 2-6 months after the re-SBRT. Initial SRT dose is 72.5% (16/22) 27 Gray (Gy) in 3 fx, 18% (4/22) 30Gy in 5fx, and 13.5% (3/22) 25Gy in 5fx. re-SRT dose is 63.5% (14/22) 27 Gy in 3 fx, 32% (7/22)30Gy in 5fx and 9% (2/22) 25 Gy in 5fx. SPINO criteria indicates, 63.5% (14/22) stable disease (including postoperative radiation cases), 9% (2/22) partial response, 13.5% (3/22) mild progression with subsequent MRI confirmed further response, and 9% (2/22) clear progression. After re-SRT, median follow up was 7 months (1-63 months). CTCAE shows 4.5% (1/22) G2 myelopathy and 4.5% (1/22) G3 myelopathy with average BED_2Gy/4Gy results of 48 Gy, 81 Gy, 84 Gy, 114 Gy, 137 Gy for SC, SC+2mm, CE, CE+2mm, and TS respectively.
Conclusion: Due to clinical treatment improvement, patients live longer with metastatic disease, hence, the need for spine retreatments. To our knowledge, this is one of the few reports revealing outcomes of SRT followed by re-SRT using 27Gy/3fx followed by 27Gy/3 fx or 30Gy/5fx for treating spine metastasis and trying to associate myelopathy with total BED doses. Our cohort shows this is a safe, effective treatment and the cohort is increasing. These treatments require multi-disciplinary care and further prospective evaluation.