LBA 27 - Evaluation of Intraoperative Cesium-131 Brachytherapy's Role in Local Control and Radionecrosis in Upfront Glioblastoma: A Case Series

Purpose/Objective(s):

Glioblastoma (GBM) remains the most common and aggressive primary malignant brain tumor in adults. Despite maximal safe resection followed by chemoradiation per the Stupp protocol, a majority of recurrences occur within 2 cm of the resection cavity, emphasizing the need for improved local control strategies. GammaTile (GT Medical Technologies Inc.) is a FDA-approved Cesium-131 brachytherapy device placed during surgery that initiates adjuvant radiotherapy immediately following tumor resection and has shown evidence of improved local control in the setting of recurrent GBM. However, limited data exists regarding the rates of local control and radionecrosis in the setting of upfront GBM patients due to short-term follow up windows.

With this study, we aim to establish a case series to determine clinical outcomes of patients with upfront GBM who received intraoperative brachytherapy with GammaTile. We hypothesize that the GammaTile local control rate will be >90% with less than 5% occurrence of Common Terminology Criteria for Adverse Events version 5.0 (CTCAE v5.0) grade 3 or greater adverse events. To test this hypothesis, we will pursue the following specific aims:

1. Determine 6- and 12-month local control rates in individuals following GammaTile placement
2. Characterize radiographic response patterns, including rates of radionecrosis as well as incidence and severity of adverse events

Materials/Methods:

A registry-based case series was conducted at Inova Schar Cancer Institute including patients with newly diagnosed, histopathologically confirmed IDH-wildtype GBM who underwent maximal safe resection with intraoperative GammaTile placement. Primary endpoints were 6- and 12-month local control. Secondary endpoints included symptomatic radiation necrosis and CTCAE v5.0 adverse events. Exploratory analyses evaluated associations between tumor volume, molecular features, and local control.

Results:

Six patients were included. Median age was 75 years, and median KPS was 75. Gross total resection was achieved in 5 of 6 patients, and 3 of 6 tumors were MGMT methylated. Local control was achieved in 83.3% of patients at 6 months and 50.0% at 12 months. Overall survival at 12 months was 66.7%. Grade 3 or greater adverse events occurred in 33.3% of patients, and symptomatic radiation necrosis occurred in 16.7%. On exploratory analysis, smaller tumor volume and MGMT methylation were associated with improved 12-month local control, though these findings did not reach statistical significance (p=0.10).

Conclusion: This case series provides early evidence supporting intraoperative GammaTile brachytherapy in newly diagnosed glioblastoma, demonstrating an 83.3% 6-month local control rate and preliminary associations between MGMT methylation, smaller tumor volume, and sustained 12-month local control. Although limited by small sample size, these hypothesis-generating findings support larger prospective studies to refine patient selection and optimize outcomes.