SURG-53. LONG TERM FOLLOW-UP OF RESECTION PLUS CESIUM-131 BRACHYTHERAPY FOR PREVIOUSLY IRRADIATED RECURRENT BRAIN METASTASES

Abstract BACKGROUND Recurrent brain metastases (rBM) after previous radiosurgery present a clinical dilemma, as the advantages of reirradiation need to be weighed against the potential of significant radiation toxicity. Salvage resection with Cs-131 brachytherapy offers improved dosimetry due to reduced integral dose to healthy brain compared to repeat radiosurgery. We previously reported initial results of rBM treated with resection and salvage Cs131 brachytherapy; we present an updated analysis of tumor control with extended follow-up. METHODS We analyzed consecutive patients with rBM previously treated with radiosurgery, who underwent salvage resection plus implantation of Cs131 seeds (GammaTile, GT Medical Technologies). The prescribed brachytherapy dose was 60 Gy at 5mm from the cavity. Median follow-up was calculated using reverse Kaplan-Meier. Local recurrence was defined by new nodular contrast enhancement with hyperperfusion within 5mm of the resection cavity. Marginal recurrence was defined as >5mm but not beyond 1cm from the cavity. Local control and overall survival (OS) from brachytherapy were analyzed using Kaplan-Meier. RESULTS Twenty-five patients underwent Cs131 implantation in 30 tumor cavities. The median presurgical rBM maximal diameter was 2.95 cm (range 1.1-6.3). The most common histology was lung adenocarcinoma (n=8, 27%) followed by breast (n=7, 23%) and renal cell (n=3, 10%). Radiographic gross- or near-total resection was achieved in 80% of lesions. The median number of Cs131 seeds implanted was 17, (range 6-30), (median strength 3.5 U/seed). With median follow-up of 37 months (95%CI:29-45), twelve and 24-month OS was 55% and 41%, respectively. Four tumors recurred (3 in-field, one marginal) for a 1- and 2-year local control rate of 87% and 81%, respectively. Data for adverse radiation effects is under analysis and will be presented. CONCLUSIONS With over 3 years of follow-up, intraoperative brachytherapy with collagen-embedded Cs131 implants was associated with durable local control for this challenging clinical scenario. A randomized Phase II trial of Cs131 vs. standard of care for rBM (NCT04690348) is actively accruing.