2598 - Intracranial Progression Following Hippocampal-Avoiding Whole Brain Radiotherapy in Patients with Brain Metastasis
Presenter(s)
E. Guvenli1, G. Chien2, N. Baughan2, H. Urquidi2, V. Xu3, C. Shen4, A. A. Weiner4, and X. S. Chen5; 1University of South Florida Morsani College of Medicine, Tampa, FL, 2University of North Carolina, Chapel Hill, NC, 3Department of Radiation Oncology, University of North Carolina School of Medicine, Chapel Hill, NC, 4Department of Radiation Oncology, University of North Carolina, Chapel Hill, NC, 5Case Western Reserve University, Cleveland, OH
Purpose/Objective(s): Hippocampal avoidance (HA) may decrease the cognitive sequelae from whole-brain radiotherapy (WBRT) for patients with brain metastasis. The efficacy of intracranial control using HA-WBRT, especially in the cold spots near the hippocampi, needs further study. The aim of this study is to quantify the risk of intracranial and peri-hippocampal progression in patients undergoing HA-WBRT.
Materials/Methods: We retrospectively identified patients who received HA-WBRT at a single institution between 2019-2024. Demographic, tumor-related (primary site, histology, number of brain metastases), and treatment variables (systemic therapy) were collected. For those with follow up imaging, brain MRI were obtained and rigidly registered to the initial radiation plan. The main outcomes of interest were intracranial progression, defined as any tumor growth in the brain after HA-WBRT, and peri-hippocampal progression, defined as tumor growth in the brain outside the prescription isodose line. Overall survival and freedom from intracranial and peri-hippocampal progression were estimated using the Kaplan-Meier method.
Results: 46 patients (29 female) were included. The most common primary sites were lung (N=19, small cell N=7), breast (N=15), and melanoma (N=6). Most patients (N=42, 91%) had three or more brain metastases prior to HA-WBRT. Ten patients (21%) received stereotactic radiosurgery prior to HA-WBRT, and 40 (87%) had systemic therapy before or after treatment. Overall survival was 83% at 6 months and 51% at 12 months. Of the 32 patients with follow up imaging, 10 had intracranial progression at a median of 7.5 months (range 3-30). All 10 patients had progression within the prescription dose, of whom 3 also had progression in the peri-hippocampal area at an interval of 3, 5 and 11 months after treatment, respectively. Of the 3 patients with peri-hippocampal progression, two had SCLC and one had melanoma. Freedom from peri-hippocampal progression was 90% at 6 months.
Conclusion: Peri-hippocampal progression after HA-WBRT may occur at a higher rate than previously assumed but often occurs in the context of distant progression in the brain. Patients with SCLC may be at a higher risk of peri-hippocampal progression after HA-WBRT. Selection criteria for candidates for HA-WBRT may require further refinement.