ESTRO 2025 - Abstract Book

S680

Clinical - CNS

ESTRO 2025

Purpose/Objective: For non-elderly glioblastoma (GBM) patients with good performance status, the standard radiation (RT) dose is 60 Gy in 2 Gy fractions, although a reduced dose of 54 Gy in 1.8 Gy fractions may be used for extensive tumor volumes to lessen side effects. This review evaluates the clinical target volume (CTV) threshold for dose reduction and compares the clinical characteristics and outcomes of patients treated with 54 Gy versus 60 Gy. Material/Methods: We analyzed 169 GBM patients treated at our center between 2019 and 2022. Univariate logistic regression (ULR) assessed CTV’s predictive value for dose reduction, while the Youden index determined the optimal threshold. Multivariate logistic regression (MLR) developed a score incorporating CTV with additional RT metrics to improve predictive accuracy. Results: Of the 169 patients included in the study, 24 received 54 Gy, while 145 received 60 Gy. The 54 Gy group more frequently had tumors involving multiple lobes, the brainstem, and both hemispheres, and more often underwent biopsy only. These patients required higher dexamethasone doses and were less likely to discontinue post-RT. The mean CTV in the 54 Gy group was 375.56 ± 279.23 cc, whereas the mean CTV in the 60 Gy group was 173.92 ± 75.32 cc. Median overall survival (OS) was 10.8 months for the 54 Gy group and 19.2 months for the 60 Gy group (HR = 0.47, p = 0.0115). Median progression-free survival (PFS) was 6 months for 54 Gy and 8.4 months for 60 Gy (HR = 0.59, p = 0.0323). Univariate analysis revealed that a dose of 60 Gy and a smaller CTV were associated with better PFS and OS. However, multivariate analysis showed that neither dose nor CTV independently predicted these outcomes. In ULR, higher CTV, gross tumor volume (GTV), and planning target volume (PTV), lower brain outside PTV (BrainMinusPTV) volume, and higher mean dose to BrainMinusPTV were associated with dose reduction to 54 Gy. CTV had a predictive power of 0.79 (0.66, 0.92), with the optimal CTV threshold for dose reduction to 54 Gy identified at 225.71 cc. In MLR, a combined score incorporating all these RT metrics showed improved predictive power of 0.84 (0.72, 0.97). The optimal threshold for this combined score was -3.364. Conclusion: This study identified a CTV threshold for dose reduction to 54 Gy in cases of extensive tumor volumes, which can inform clinical practice. Patients treated with this reduced dose had poor baseline prognostic factors and unfavorable outcomes.

Keywords: glioblastoma, dose reduction

1686

Digital Poster The importance of being united: impact of neuro-oncology multidiciplinary boards on radiation oncology decision making - a one-year review Silvia Mariani 1 , Silvia Chiesa 1 , Ciro Mazzarella 1 , Antonella Martino 1 , Nicola Dinapoli 1 , Serena Bracci 1 , Natalia Barogi 2 , Lucia Di Maio 2 , Rosellina Russo 1 , Giuseppe Maria Di Lella 1 , Quintino Giorgio D'Alessandris 3 , Giuseppe Maria Della Pepa 3 , Valeria Masiello 1 , Roberta Bertolini 1 , Elisa Meldolesi 1 , Mariangela Massaccesi 1 , Lana Smiljanic 2 , Francesco Giuseppe Ciardo 2 , Fabio Marazzi 1 , Liverana Lauretti 3 , Marco Gessi 4 , Simona Gaudino 1 , Luca Tagliaferri 1 , Alessandro Olivi 3 , Maria Antonietta Gambacorta 1 1 Department of Diagnostic imaging, Radiation Oncology and Hematology, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 2 Department of Diagnostic imaging, Radiation Oncology and Hematology, Università Cattolica del Sacro Cuore, Rome, Italy. 3 Department of Neuroscience, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 4 Department of Neuropathology, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy