2041 - Risk Factors for Treatment-Related Effects in Brainstem Metastases Following Stereotactic Radiosurgery
Presenter(s)
D. Colson-Fearon1, T. Ford2, S. Perni3, M. F. F. McAleer4, D. N. Yeboa5, T. Beckham4, M. C. Tom4, T. A. Swanson6, C. Wang4, C. Chung4, A. J. Ghia4, J. Li4, D. Kaya7, R. Eldaya8, J. S. Weinberg9, F. Lang10, B. J. O'Brien11, T. M. Briere12, D. Mackin13, and B. De4; 1Johns Hopkins University School of Medicine, Baltimore, MD, 2University of Texas MD Anderson Cancer Center, Houston, TX, 3Columbia University Vagelos College of Physicians and Surgeons, New York, NY, 4Department of CNS Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 5MD Anderson Cancer Centre, Houston, TX, 6University of Texas Medical Branch, Galveston, TX, 7MD Anderson Cancer Center, Neuroradiology department, houston, TX, 8Department of Neuroradiology, Division of Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, 9Department of Neurosurgery, The University of Texas MD Anderson Cancer Center, Houston, TX, 10Department of Neurosurgery, University of Texas MD Anderson Cancer Center, Houston, TX, 11Department of Neuro Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 12MD Anderson Cancer Center, Houston, TX, 13Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s):
Stereotactic radiosurgery (SRS) is a mainstay in management of brain metastases; however, treatment of brainstem lesions remains challenging, as even modest treatment-related effects (TAEs) may result in severe neurologic injury. Data to inform risk-adapted treatment strategies are limited. We sought to characterize the incidence, timing, and clinical outcomes of TAEs after SRS for brainstem lesions and to identify clinical and treatment predictors of toxicity.Materials/Methods:
Patients with metastatic brainstem lesions treated with Gamma Knife or linac-based SRS, delivered in single- or multi-fraction regimens at MD Anderson Cancer Center between January 2010 and July 2025, were retrospectively reviewed. Demographic, treatment, dosimetric, and outcome data were collected. TAE was defined as persistent lesion enlargement with new perilesional edema and low clinical suspicion for progression after multidisciplinary review, supported by absence of perfusion elevation on MRI, new steroid requirement, and/or new neurologic symptoms. Associations between clinical or dosimetric variables and TAE were evaluated using logistic regressions.Results:
A total of 311 patients with 366 brainstem metastases were identified. Radiographic TAEs occurred in 33 lesions (9.0%), affecting 26 patients (8.4%), of whom 21 (6.8%) were symptomatic. 352 of the lesions were treated in a single fraction, while 14 lesions were treated using fractionated SRS. Median follow-up among all patients after treatment was 48.5 months (IQR, 16.4–90.0), and median overall survival was 11 months (IQR, 5.07–32.2). The median time to onset of TAE was 3.7 months (IQR, 1.9–10.0). On multivariable analysis, lower prescription dose (OR 0.74, 95% CI 0.61–0.91) and larger target volume (OR 1.31, 95% CI 1.10–1.56) were associated with TAE. Fractionation was not significantly associated with TAE (OR 5.09, 95% CI 0.26–98.4), although confidence intervals were wide. One- and two-year local control rates were 96.4% (95% CI 92.4–98.3%) and 95.3% (95% CI 90.3–97.7%), respectively. There were no significant differences in local control between linac-based and Gamma Knife platforms (HR 3.05, 95% CI 0.39–24.1) nor between single- and multi-fraction regimens (HR 2.55, 95% CI 0.32–20.1).Conclusion:
SRS for brainstem metastases achieved excellent local control but carried a measurable risk of TAE. Larger target volumes and lower prescription dose were associated with increased toxicity risk, with the relationship between lower dose and TAE likely attributable to dose de-escalation in larger or high-risk lesions. Fractionation was not significantly associated with TAE. These findings highlight the narrow therapeutic window of brainstem SRS and underscore the need for refined dose–volume constraints to optimize safety and improve the therapeutic ratio. Ongoing analyses will focus on dose–volume histogram metrics to better define tolerable thresholds for critical brainstem substructures.