ESTRO 2025 - Abstract Book

S1492

Clinical – Mixed sites & palliation

ESTRO 2025

1417

Digital Poster A review of 130 Cyberknife spinal metastasis SABR treatments at one centre to assess risk of spinal cord toxicity Timothy Jackson, Jenny Sherriff, Talha Maqsood Radiotherapy, Queen Elizabeth Hospital, Birmingham, United Kingdom Purpose/Objective: Recent publications[1][2] have suggested spinal cord constraints for spinal cord Stereotactic Ablative Body Radiotherapy (SABR), lower than has previously been published such as in TG101 [3]. Within the UK there is increasing interest in spinal SABR. To date the majority of published studies considering spinal SABR toxicity are limited by small numbers of patients. The 2022 dose consensus[1] discusses 7 studies in the literature, with 2 over 100 patients, but includes 4 less than 30 patients. The presented series includes 130 treatments of 119 patients, with a minimum of 18 months follow up. This is a valuable addition to the literature due to the precise treatment on the Cyberknife platform, high resolution pre treatment imaging, and intrafraction target tracking ensuring dose reported is known accurately. The significant number of patients treated and quality of follow up allows confidence in conclusions drawn. Material/Methods: All structures were contoured using CT, t1 VIBE and t2 SPACE MRI scans with 1mm resolution, according to UK SABR consortium guidelines. The target is at minimum the full vertebral body. Plan prescription dose range was 24 - 27Gy in 3 fractions and TG101 tolerances used. Mean PTV volume was 56.8cc. Cord was grown by 2mm isotropically to create CordPRV. During treatment delivery, Cyberknife spine tracking had an end-to-end accuracy averaging 0.7mm for these patients. Images were taken and live treatment correction was applied every 30-45 seconds throughout treatment. Plan dose information was recorded. Patient hospital clinic appointments and GP records were checked for toxicity and this was recorded. A minimum of 18 months follow up was required. Results: 10 patients died prior to 18 months after treatment or were lost to follow up, with none reporting myelopathy. 109 patients had records from phone clinic, hospital clinic attendance, or GP records where patients were assessed. No cases of myelopathy were recorded. In 49/130 patient treatments, CordPRV dose was above recent tolerance 2022 dose consensus tolerance[1] but below TG101 tolerance[3]. In 109/130 patient treatments, spinal canal was above 22Gy(0.1cc), and within [1] and [3] 24Gy tolerance. Conclusion: 130 spinal treatments were planned above recent tolerances with 5% risk of myelopathy[1] and delivered with no myelopathy seen. Given the low number of spinal patient series in the literature, and the high resolution, precise treatment, and intrafraction tracking for these patients, this is very valuable for understanding safe doses for treatment near the spinal cord. References: [1] Diez, P., et al. 2022. UK 2022 consensus on normal tissue dose-volume constraints. Clinical Oncology , 34 (5), pp.288-300. [2] Sahgal A et al., Spinal cord dose tolerance to stereotactic body radiation therapy. Int J Radiat Oncol Biol Phys 2021 [3] Benedict, S et al. 2010. Stereotactic body radiation therapy: the report of AAPM Task Group 101. Medical physics , 37 (8), pp.4078-4101. [4] E. Katsoulakis et al, A Detailed Dosimetric Analysis of Spinal Cord Tolerance in High-Dose Spine Radiosurgery, International Journal of Radiation Oncology*Biology*Physics, Volume 99, Issue 3 (2017) Keywords: SBRT, myelopathy, Cyberknife