S379
Clinical - CNS
ESTRO 2026
promotor might benefit from normofractionated treatment with concomitant systemic therapy. Keywords: Glioblastoma, re-irradiation
Department of Radiation Oncology, Comprehensive Cancer Center Vienna, Medical University of Vienna, Vienna, Austria
Purpose/Objective: Normofractionated re-irradiation might be
Digital Poster 3339 Feasibility of Margin Reduction to the
radiobiologically advantageous due to a favourable ratio of biological equivalent dose to the tumour while keeping normal tissue constraints. However, the overall treatment time is of concern in patients with limited prognosis at re-irradiation of glioblastoma. Material/Methods: We analysed 79 consecutive patients who underwent normofractionated re-irradiation of progressive, IDH- wildtype glioblastoma to 36-40 Gy from 2013 to 2024. Patient, tumour and treatment characteristics were analysed and correlated with progression-free survival and overall survival after re-irradiation. Results: Patient and tumour characteristics are shown in Table 1. Median PFS was 4 months. Median OS was 9 months, with only 6% of patients surviving more than two years. Exploratory univariable analysis showed OS was longer in patients with an interval >16 months between radiotherapy courses (15 vs 8 months, p<0.001), presence of MGMT-promoter methylation (13 vs 9 months, p=0.011), age <60 years (12 vs 8 months, p=0.031), PTV size of 100 cm ³ or less (13 vs 8 months, p=0.037) and for patients receiving GTR (18 months) as compared to STR (10 months, p=0.029) or no resection (8 months, p=0.012). Patients receiving concomitant systemic therapy had longer median OS than those who did not, but only if MGMT-promoter methylation was present (18 vs 6 months, p=0.001).Table 1: Patient and treatment characteristics
Pseudocapsule Border in Fractionated Stereotactic Radiotherapy of Acoustic Neuroma: First Three- Year Evaluation Gyöngyi Kelemen 1 , Eszter Bimbó 1 , Ágnes Dobi 1 , Aliz Nikolényi 1 , Linda Varga 1 , Em ő ke Borzási 1 , Viktor Paczona 1 , Emese Fodor 1 , Anikó Maráz 1 , Judit Oláh 1 , Katalin Hideghéty 1,2 1 University of Szeged, Albert Szent-Györgyi Clinical Center, Szeged, Hungary. 2 Albert Szent-Györgyi Clinical Center, Department of Oncotherapy 2 ELI-ALPs, Non- profit LTD, Szeged, Hungary Purpose/Objective: Stereotactic radiotherapy (SRT) achieves excellent control in acoustic neuroma (AN) while preserving neurological function. However, defining an optimal planning target volume (PTV) remains critical due to the close proximity of the tumor to the brainstem. Histopathological studies describe a fibrous pseudocapsule surrounding AN that delineates the tumor from adjacent neural tissue. Conventional 2–3 mm GTV–PTV margins may therefore extend beyond this boundary and increase the risk of brainstem toxicity. Moreover, modern SRS planning inherently delivers spatially differentiated dose distributions, with 85–90% of the prescribed dose typically deposited within 1 mm outside the PTV, which may still sterilize microscopic extensions within the pseudocapsule. After observing severe necrosis in 3 of 14 patients ( ≈ 20%) treated with standard margins, we adopted a reduced-margin approach (0 to − 1 mm). This study presents the first outcome evaluation after ≥ 3 years’ follow-up. Material/Methods: We retrospectively analyzed 22 AN patients treated with image-guided, fractionated SRT (3–5 fractions, 4–9 Gy per fraction) between 2016–2024. GTV was defined as the contrast-enhancing lesion on MRI, corresponding to the tumor within its pseudocapsule. Margins ranged from − 1 mm to +3 mm. Follow-up MRI was performed every 3–6 months initially and annually thereafter. Local control, surgery, and histologically confirmed necrosis were assessed. Results: Median age was 63 years (range 20–81). Most treatments used a 2 mm margin (n = 14), 0 mm in 5, and − 1 mm in 3. Median follow-up was 7.0 years (range 2.5–9.1). Local control was 83% (partial response 5, stable disease 13). Four patients (18%)
N = 79Median age at recurrence in months (range)59 (34-87)Median time between radiotherapy courses in
months (range)16 (2-44)MGMT-promoter methylated39 (49%)Resection status at
recurrenceGross total resection (GTR)21 (27%)Subtotal resection (STR)19 (24%)No resection39 (49%)Median size of the planning target volume in cm ³ (range)100 (30-351)Radiotherapy techniqueIntensity modulated radiotherapy69 (87%)3D-conformal radiotherapy10 (13%)Prescribed radiotherapy dose and fractionation36 Gy/18 fractions70 (89%)40 Gy/20 fractions9 (11%)Concurrent systemic therapy using temozolomide or lomustine60 (76%)Radiotherapy course completed as prescribed78 (99%) Conclusion: Median progression-free survival and overall survival were very limited and comparable with the current literature. Thus, our data seem to support the current recommendation of hypofractionated re-irradiation. However, younger patients with a longer time between first and second radiotherapy with methylated MGMT-
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