ESTRO 2025 - Abstract Book

S761

Clinical - CNS

ESTRO 2025

chemoradiation was not associated with improved median OS (12.9 vs. 9.5 months, p = 0.31) or PFS (5.5 vs. 4.6 months, p = 0.48) compared to re-irradiation alone. Subanalysis of chemoradiation for GBM revealed a significant improvement in OS (14.6 vs. 7.2 months, p = 0.01) and PFS (32 vs. 22.0 months, p = <0.0008). The primary tumor type and grade significantly influenced OS (p = 0.011) and PFS (p < 0.001). Patients aged ≥50 had a shorter median OS compared to younger patients (8 vs 13.8 months, p < 0.004). Additionally, patients treated with dexamethason at recurrence had a median OS of 8.6 months compared to 12.8 months for those who did not (p = 0.006). The overall incidence of latetoxicity (including radionecrosis) was 36.8%, and the treatment was generally well-tolerated. Conclusion: Repeated concurrent chemoradiation did not make a significant difference in survival over re-irradiation alone in the overall patient population. However, a subanalysis of the GBM patients showed that repeat concurrent chemoradiation improved OS compared to re-irradiation alone. To further support these findings, more prospective research is needed.

Keywords: Re-irradiation, Gliomas, recurrent

4373

Digital Poster Short term clinical outcomes after Linac based Stereotactic Radiosurgery Treatment of Deep Brain Arteriovenous Malformations (AVMs) Mir Ahmad Mousavizadeh 1 , Maryam Moshtaghi 1 , Guive Sharifi 2 , Zohreh Azma 1 , Sajjad Khanbabazadeh 2 , Amir Hakimi 1 , Fatemeh Ghahramani 1 , Hamed Mirzaei 1 , Farahnaz Rahimi 1 1 Radiotherapy department, Erfan Neyayesh hospital, Tehran, Iran, Islamic Republic of. 2 Neurovascular intervension, Iran University of Medical sciences, Tehran, Iran, Islamic Republic of Purpose/Objective: Stereotactic radiosurgery (SRS) has demonstrated excellent treatment outcomes for small- and medium -sized lesions with the reported obliteration rates of about 80 - 90 % within 2 to 3 years [1]. However, the treatment of Deep Brain Arteriovenous Malformations (AVMs) located in insula, basal ganglia, and thalamus poses significant challenges due to increased risk of unfavorable complications in the brain, and need more considerations [2,3]. Staged techniques of radiosurgery including volume staged and dose staged and also hypo fractionated radiosurgery (HSRT) are commonly used for treatment of large lesions [4, 5]. The aim of the present study is to evaluate the short- term clinical results of the SRS/HSRT treatment of large AVMs. Material/Methods: Eight patients with large AVMs treated by Linac-based SRS/HSRT technique between January 2021 and 2023 were retrospectively evaluated. The prescription dose was 16 to 30 Gy in 1 to 5 fractions with an 80% prescription isodose line. Lesion dose response, such as nidus obliteration, and volume reduction evaluated through periodic magnetic resonance imaging (MRI) and cerebral angiography, were assessed. Probable acute and long-term toxicity were also monitored during follow- up. Results: The mean age of the patients was 18.5 ± 9 years. With a median follow-up of 23 months (range: 12–34), no patient had achieved complete obliteration. The mean volume of the gross tumor volume (GTV) before treatment was 13. 5 ± 7.5 cm 3 . GTV volume reduction averaged approximately 43%. GTV volume reduction was more pronounced in patients treated by single- fraction SRS or volume staged technique. No HSRT-related complication was observed clinically or radiologically.