Abstract Cesium-131 brachytherapy (GammaTileTM) is a relatively new form of surgically targeted radiation therapy for recurrent glioblastoma. While seed migration is a well-documented complication of solid tumor brachytherapy, it has not been reported in the treatment of glioblastoma. Here, we describe a rare occurrence of seed migration in a 71-year-old patient treated for recurrent left temporal lobe glioblastoma. The GammaTile is comprised of a resorbable collagen matrix containing four titanium-encapsulated radioactive Cs-131 seeds. Each seed emits a localized dose of radiation with a 9.7-day half-life. To prevent displacement from the resection cavity, oxidized regenerated cellulose (SurgicelTM) was applied to the cavity surface under the tiles and fibrin sealant (TisseelTM) was applied over the tiles. Margins of the lateral ventricles were not breached during the surgery and surface was non-ulcerated. The tiles remained in place on follow-up imaging for at least 7 weeks. At least 97% of the prescribed dose was delivered before seed migration. Bevacizumab systemic treatment was initiated. Abdominal CT obtained after 3 months incidentally noted migration of 2 seeds to the sacral spinal canal. Additional seeds had migrated to the suprasellar region, left lateral ventricle, and lateral cerebellomedullary cistern. Despite seed migration, the patient maintained progression-free survival for at least 10 months, with at least 30 months of overall survival from the time of diagnosis. Although the patient did not experience any symptoms related to seed migration, this has the potential to cause radiation-related toxicity to healthy tissue, particularly if it occurs early after surgery. The use of bevacizumab may have contributed to penetration of the lateral ventricle. Despite meticulous surgical technique, the potential for seed migration should be considered during treatment planning when using anti-angiogenic therapies. Further research is needed to better understand the factors contributing to seed migration and to develop strategies for minimizing this risk.
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