INNV-60. First use of Cesium-131 embedded collagen tiles for brachytherapy in the spine: combined surgical resection and brachytherapy for recurrent rectosigmoid adenocarcinoma metastasis to the sacrum

Abstract BACKGROUND The utilization of Cesium-131 embedded collagen tiles (Cs131CT) for high-dose rate brachytherapy has thus far primarily been implanted intracranially. Advantages of Cesium-131 include less tissue penetration thus lowering the risk of damage to nearby organs and neural elements. Utilization of brachytherapy allows for a surgically targeted radiation source that takes effect immediately upon intraoperative implantation. We aim to present the first utilization of Cs131CT brachytherapy in the spine. METHODS Patient selection included recurrent metastatic cancer resistant to multiple lines of chemotherapy, biologic therapy, and radiation with symptomatic metastasis to the lumbosacral spine. A 55-year-old male with symptomatic lumbosacral compressive polyradiculopathy from locally advanced and recurrent rectosigmoid adenocarcinoma involving the sacrum and lumbosacral nerve roots was selected via multidisciplinary discussion amongst our institutional Spine Tumor Board. Options included observation with expected disease progression, sacrectomy, or off-label compassionate Cs131CT brachytherapy with tumor debulking and partial sacrectomy. A shared-decision was made to undergo L5-S3 decompression and partial sacrectomy with tumor debulking and placement of Cs131CT brachytherapy. RESULTS A 3D model of the patient’s spine with the tumor included was created to simulate the operation in a lab setting prior to surgery. This allowed for estimation of the local radiation dose delivered and to develop a strategy to avoid damage to the cauda equina. Surgery was then performed with successful debulking of the tumor and circumferential decompression. Cs131CT were then placed with adequate distance from the neural elements. Post-operative dosimetry calculation from the patient’s imaging was 106.4Gy, which was within 10% of the predicted Cs131CT dosimetry. Three- and six-month post-operative MRI was completed with no obvious recurrence at the area of intended brachytherapy. CONCLUSIONS We present the first ever use of Cs131CT brachytherapy in the spine. Utilization of a pre-surgical model to determine feasibility and safety, as well as establishment of a multi-disciplinary team, were critical in providing a new alternative for a patient faced with limited treatment options.