S947
Clinical - Non-malignant & functional radiotherapy
ESTRO 2026
Material/Methods: A retrospective review was conducted of patients diagnosed with VS/AN between January 2013 and January 2021 at a single institution. Data were collected on demographics (e.g., age, sex), prior observation or surgery, tumor characteristics (location, size in X/Y/L dimensions), cranial nerve involvement, and baseline symptoms (tinnitus, hearing impairment, pain). Audiometry results (normal vs. impaired hearing) were recorded at baseline and follow-up. Treatment details encompassed radiotherapy dose (single-fraction vs. multi-fraction), technique (Conformal Arcs, Conformal Beams, RapidArc/VMAT), and therapy duration. Local control was estimated via Kaplan–Meier analysis; log-rank and chi-square ( χ² ) tests were used for subgroup comparisons, with p<0.05 considered significant. Results: Forty-five patients (mean age 46.53 ± 12.87; 42.2% male) were identified. Most tumors were unilateral (97.8%). Five patients (11.1%) had prior surgery. Baseline hearing was impaired in 86.0%, and significant pain was reported in 83.3%. Median tumor dimensions were 18.5 mm (X), 16.0 mm (Y), and 13.5 mm (L). Cranial nerve involvement was 10.0%. Of 44 patients (97.8%) who received radiotherapy, 11.3% underwent single-fraction SRS (12–13 Gy), 81.8% had 25 Gy in 5 fractions, and 6.9% received 50.4–54 Gy over 26–30 fractions. After a median follow-up of 2.55 years, 63.2% of tumors were stable, 31.6% decreased, and 5.3% progressed. Hearing was preserved in 97.4%, with only 2.6% new hearing loss. Intratumoral necrosis (51.4%) was considered a tumor response. No grade ≥ 3 adverse events or permanent cranial nerve deficits occurred. LC did not differ by fractionation, but a nonsignificant trend (p=0.062) suggested larger tumors and greater cranial nerve involvement may predispose to progression. Conclusion: SRS and fSRS yielded favorable tumor control and hearing preservation for VS/AN in this cohort, with minimal severe toxicity. Although fractionation schedule did not significantly affect LC, there was a nonsignificant trend indicating that larger tumors and greater cranial nerve involvement might increase progression risk. Further prospective studies are warranted to refine fractionation strategies. References: Flickinger JC, Kondziolka D, Niranjan A, et al. Acoustic neuroma radiosurgery with marginal doses of 12–13 Gy. Int J Radiat Oncol Biol Phys. 2004;60(1):225–230. Meijer O, Vandertop W, Baayen J, Slotman B. Single- fraction vs fractionated linac-based stereotactic radiosurgery for vestibular schwannoma. Int J Radiat Oncol Biol Phys. 2003;56(5):1390–1396. Morimoto M, Yoshioka Y, et al. Hypofractionated stereotactic radiation therapy in three to five fractions for
At six and twelve months post-STAR, 79% and 56% of patients were still under follow-up, with survival probabilities of 88% and 79%, respectively. Conclusion: Despite incomplete follow-up, the interim analysis of the STOPSTORM registry highlights that STAR effectively reduces VT burden with few treatment- related SAEs. Overall survival is promising but requires longer follow-up for confirmation. Keywords: STAR, ventricular tachycardia, STOPSTORM Digital Poster 2587 Outcomes and Toxicity of Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy for Vestibular Schwannomas: A Saudi Institutional Cohort Nwaf I Alkhanein, Zaid A Majeed, Nagib A AlDobai, Ahmad M Maklad, Yasser S Bayoumi, Hossam Alassaf Radiation Oncology, King Fahad Medical City, Riyadh, Saudi Arabia Purpose/Objective: Vestibular schwannomas (VS), also known as acoustic neuromas (AN), are benign tumors arising from the eighth cranial nerve. Treatment options include microsurgical resection, stereotactic radiosurgery (SRS), fractionated stereotactic radiotherapy (fSRS), and observation. While SRS/fSRS are effective, the optimal fractionation strategy remains unclear. This study evaluated clinical outcomes and toxicity in a Saudi cohort with VS. The primary endpoint was local control (LC), defined as the time from treatment completion to radiological tumor progression. Secondary endpoints included toxicity and the impact of fractionation on tumor control.
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