ESTRO 2025 - Abstract Book

S655

Clinical - CNS

ESTRO 2025

Material/Methods: Imaging and clinical data were reviewed for consecutive patients with LMD from solid tumors, who completed a course of pCSI at a single tertiary care institution between 2022-2024. Toxicity was reported from treatment start and up to 3 months post-pCSI using Common Terminology Criteria for Adverse Events (CTCAE version 5). OS and PFS were assessed using the Kaplan-Meier method for patients who had at least one follow-up visit. Results: The study cohort included 45 patients; the median age was 62 years (range: 23-82), most were female (84%), and median KPS was 90 (range 70-100). The most common primary tumors were breast (n=29) and lung (n=13), and a majority had prior radiotherapy to the brain or spine (58%). pCSI was delivered using an intensity modulated proton therapy (IMPT) technique to a dose of 30 Gy in 10 fractions for all patients; twelve patients (27%) received concurrent systemic treatment. The median time from LMD diagnosis and CT simulation to pCSI start was 19 and 8 days, respectively. Overall, 18 patients (40%) developed non-hematologic grade 2 toxicity comprising of alopecia (14, 31%), fatigue (7, 16%), anorexia or nausea (4, 9% each), and headache (1, 2%); no grade 3+ non-hematologic adverse events were reported. Grade 2, 3, and 4 worst hematologic toxicity was observed in 5 (11%), 21 (47%), and 2 (4%) patients, respectively; lymphopenia was the most common grade 3 toxicity (98%) while grade 4 toxicities included lymphopenia and neutropenia (1, 2% each). Grade 2+ hematologic toxicity rates were similar in those receiving pCSI with or without concurrent systemic therapy (50% vs. 67%, p=0.312). At a median follow-up of 5.0 months (range: 1.8-26.6) for patients included in the efficacy analysis (n=35), the median CNS-PFS was 8.1 months (95% CI: 3.9-12.3), and the median OS was 10.1 months (95% CI: 1.4-18.8).

Conclusion: Treatment with pCSI is feasible in real-world settings outside clinical trials, yielding similar efficacy and an acceptable toxicity profile, with rare grade 4 hematologic toxicity and no grade 3+ non-hematologic toxicity.

Keywords: Leptomeningeal, craniospinal irradiation, protons

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Poster Discussion Contrast-enhancing lesions induced by CNS-directed intensity modulated proton therapy: imaging characterization with relative cerebral blood volume Omer Gal 1 , jen Yu 1 , Minesh P. Mehta 1 , Charif Sidani 2 , Kevin J. Abrams 2 , Matthew D. Hall 1 , Robert H. Press 1 , Yazmin Odia 3 , Michael W. McDermott 4 , Zachary Fellows 1 , Andrew Wroe 1 , Alonso N. Gutierrez 1 , Rupesh Kotecha 1 1 Department of Radiation Oncology, Miami Cancer Institute, Miami, USA. 2 Department of Radiology, Baptist Health South Florida, Miami, USA. 3 Department of Neuro-Oncology, Miami Cancer Institute, Miami, USA. 4 Department of Neurosurgery, Miami Cancer Institute, Miami, USA Purpose/Objective: Patients with CNS/skull base tumors treated with intensity modulated proton therapy (IMPT) may develop intracranial lesions characterized as radiation-induced contrast enhancement (RICE). Differentiating these lesions from tumor progression using standard imaging modalities remains challenging. The objective of this study was to elucidate the role of relative cerebral blood volume (rCBV) in characterizing RICE lesions and predicting their trajectory and outcome. Material/Methods: Data were reviewed for consecutive patients treated at a single tertiary care institution between 2017-2023 with IMPT for primary CNS/skull base tumors. Relative cerebral blood volume (rCBV) maps were generated from dynamic susceptibility contrast (DSC) perfusion MRI scans during follow-up. RICE lesions ≥8 mm were normalized to the