S859
Clinical - Mixed sites & palliation
ESTRO 2026
Metastasis Surgery: Clinical Outcomes and Challenges Robert Förster 1,2 , Paul Windisch 1,2 , Daniel Rudolf Zwahlen 1 , Christina Schröder 1,2 1 Department of Radiation Oncology, Cantonal Hospital Winterthur, 8401 Winterthur, Switzerland. 2 Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, 3010 Bern, Switzerland Purpose/Objective: Postoperative radiotherapy (RT) to resection cavities following resection of brain metastases (BMs) is a well- established strategy to improve local control. However, several factors- including variable target delineation, evolving postoperative anatomy, and large cavity volumes remain challenging. This retrospective study evaluated treatment outcomes, local recurrence rates, and radiation necrosis (RN) incidence in patients treated with local RT to resection cavities. Material/Methods: We retrospectively reviewed data from patients who received RT to resection cavities after surgical removal of brain metastases from solid tumors between 2018 and 2024 (widespread implementation of stereotactic radiotherapy (SRT) at our center). Patient characteristics, courses, fractionation, rate of RN, local recurrence and re-treatment rates were analysed. Results: A total of 47 patients (53% male, 47% female) underwent RT to 54 resection cavities, with 10 patients receiving re-irradiation (67 total treatment plans). Median age at first RT was 64 years (range 43-77). The most frequent primary tumor was non-small cell lung cancer (38.3%), followed by breast cancer (12.8%). The most common RT regimens were 30 Gy/5 fractions (26.9%) and 30 Gy/6 fractions (47.8%). In-field re- irradiation was performed in eight patients; one patient each underwent two and three re- irradiations.Median cranial radiological follow-up was 17 months (range 1-79), with 28 patients followed for ≥ 12 months. Median overall survival (OS) was 26.3 months (95% CI 30.5-133.5), with 1- and 2-year OS rates of 89.6% and 71%, respectively. Local failure occurred in 12 cavities (22.2%), with 1- and 2-year local control rates of 82.3% and 70%. In case of in-field recurrence, eight lesions were treated with local re- irradiation, two received further resection followed by re-irradiation and two were treated with WBRT (additional out of field failure).RN developed in 18 cavities (33.3%, 4 after re-irradiation), including 9 cases (16.7%) of grade ≥ 2 RN. Median time to RN was 15 months (range 2-79); for grade ≥ 2 RN, it was 7 months (range 2-79).Distinguishing RN from local recurrence proved difficult, despite the use of advanced imaging
(functional MRI and/or FET-PET) in 14 cases. In 8 lesions, differentiation remained inconclusive. Conclusion: In this cohort there were moderate rates of both local recurrence and high-grade RN following RT to resection cavities-particularly in patients with longer follow-up. This shows the need for optimized treatment strategies and reliable imaging tools to distinguish between RN and tumor recurrence. As survival improves, these challenges will become increasingly relevant, necessitating continued research and clinical refinement. Keywords: SRT, radionecrosis, brain metastasis Digital Poster 328 Efficacy of Targeted Osmotic Lysis for Advanced Carcinomas Dennis J Paul 1 , Harry J. Gould 2 1 Pharmacology and Experimental Therapeutics, LSU Health Sciences Center, New Orleans, USA. 2 Neurology, LSU Health Sciences Center, New Orleans, USA Purpose/Objective: Purpose/Objective: Aggressive carcinomas overexpress cell-surface voltage-gated sodium channels (VGSCs) by 3- to 20-fold and RNA up to 1800- fold. Melanomas and Glioblastoma multiform also overexpress VGSCs. Others have attacked the overexpressed VGSCs but produced neural and cardiovascular adverse effects. By contrast, in a technology that we call targeted osmotic lysis (TOL), we stimulate VGSC activity using a pulsed electric field while blocking sodium pumps with digoxin. When sodium enters cells through open channels down a 30:1 concentration gradient for sodium, but is not returned to the extracellular matrix, water follows the sodium and produces a selective osmotic lysis of cells
that overexpress VGSCs. Previously, we have demonstrated efficacy in cultured cells, mice, companion animals, and two humans under
Emergency Use and 45 in offshore clinical trials. In canine and feline companion animals, we showed efficacy in breast, lung, orofacial, colorectal, and mast cell cancers, and that resistance to the treatment does not develop. Material/Methods: Materials and Methods: In this trial, we accept patients that overexpress VGSCs as verified by immunohistofluorescent labeling of a biopsy. We treat subjects for two consecutive days for two hours each day, repeated one and two weeks later. The subjects prepare for treatment by taking a prescribed dose of
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