Initial Outcomes of GammaTile Brachytherapy From a Single Institution: A Case Series

GammaTile (GT Medical Technologies, Inc., Tempe, AZ) is a bioresorbable, collagen-based brachytherapy device embedded with cesium-131 (Cs-131) seeds that is placed within the resection cavity at the time of surgery, delivering the majority of its dose before wound healing would otherwise delay external beam radiation.It has been increasingly adopted for newly diagnosed and recurrent malignant brain tumors, yet real-world experience across tumor types remains limited.We report a single-institution case series of four consecutive patients who underwent maximal safe resection followed by GammaTile implantation: a newly diagnosed glioblastoma, a human epidermal growth factor receptor 2-positive breast cancer brain metastasis, a pulmonary adenocarcinoma cerebellar metastasis, and a non-small cell lung carcinoma metastasis.All targets were prescribed 60 Gy at a 5 mm depth.In one patient, two lesions were treated concurrently with GammaTile and ZAP-X stereotactic radiosurgery, where tiles were deliberately arranged to spare the brainstem.In this limited series, outcomes varied widely and appeared to reflect baseline tumor biology rather than a uniform treatment effect.The two patients with newly diagnosed metastases achieved durable local control, including marked cavity regression at three months and radiographic stability through 13 months, with prompt resumption of systemic therapy.The glioblastoma demonstrated new nodular enhancement at one month that could not be distinguished from pseudoprogression on structural imaging, and the high-burden lung metastasis progressed with leptomeningeal dissemination despite combinedmodality treatment.Adverse events, a pseudomeningocele and intraventricular hemorrhage with hydrocephalus, were manageable and largely attributable to surgery or disease.This series illustrates the feasibility, safety, and integration of GammaTile with chemoradiation and stereotactic radiosurgery, while highlighting the challenges of early post-implant imaging interpretation and the limits of local therapy in aggressive, disseminated disease.