ESTRO 2025 - Abstract Book

S646

Clinical - CNS

ESTRO 2025

fractions, 2 Gy per fraction for 5 weeks, followed by Phase 2- 10 Gy in 5 fractions, 2Gy per fraction over 5 days) to surgical cavity and any post contrast T1 enhancement with hippocampal sparing followed by Temozolamide on maintenance dose of 150-200mg/m 2 for 5 days on 28 days cycle for 6 cycles. Patients were evaluated using MRI and DOPA-PET CT, parameters such as tumor volume, ADC values and SUV (Standardized uptake value) and recurrences were analyzed and compared with pre-treatment values. Results: Of the 135 patients analyzed, pre-treatment mean tumor volume (MTV) was 48.70±3.79. MTV was 31.19 ±3.12 with 3DCRT, 25.74 ±2.91 with IMRT and 22.84 ± 2.82 with Helical Tomotherapy at 1 year post treatment. The mean ADC value prior to treatment was 0.71 ± 0.1. After treatment, the mean ADC values were 1.20 ± 0.91 with 3DCRT, 1.37 ± 0.81 with IMRT, and 1.65 ± 0.87 with Helical Tomotherapy. DOPA PET-CT was done with MRI and Mean SUV values before treatment were 3.46, while post-treatment mean SUV values were 2.83, 2.67 and 2.55 in patient treated with 3DCRT, IMRT and Helical Tomotherapy respectively. Median survival was comparable amongst the groups with duration of 18.2 months, with progression free survival of 9.6 months. MRI observations showed 19, 15 and 7 in-field recurrences with 3DCRT, IMRT and Tomotherapy respectively. Marginal field recurrence were seen in 2 patients treated with 3DCRT, 1 patient with IMRT and none with Tomotherapy. Out of field recurrence were seen in 7 patients with 3DCRT, 3 patients with IMRT and in 1 patient with Tomotherapy. On analysis of imaging parameters amongst treatment cohorts, helical tomotherapy outperformed IMRT and 3DCRT, however IMRT was superior to 3DCRT. A higher recurrence rate was observed with 3DCRT followed by IMRT, whereas those who received Helical Tomotherapy experienced fewer recurrences. Conclusion: Helical Tomotherapy is a superior modality of radiation therapy in glioblastoma, when compared to IMRT and 3DCRT,demonstrating greater tumor parameter reduction on imaging and a lower recurrence rate. References: Xu, S.; Frakulli, R.; Lin, Y. Comparison of the Effectiveness of Radiotherapy with 3D-CRT, IMRT, VMAT and PT for Newly Diagnosed Glioblastoma: A Bayesian Network Meta-Analysis. Cancers 2023 , 15 , 5698. https://doi.org/10.3390/cancers15235698. MacDonald SM, Ahmad S, Kachris S, Vogds BJ, DeRouen M, Gittleman AE, DeWyngaert K, Vlachaki MT. Intensity modulated radiation therapy versus three-dimensional conformal radiation therapy for the treatment of high grade glioma: a dosimetric comparison. J Appl Clin Med Phys. 2007 Apr 19;8(2):47-60. So Hwa Mun et al, Recurrence pattern of glioblastoma treated with intensity-modulated radiation therapy versus three-dimensional conformal radiation therapy , Oncology Journal 2024; 42(3): 218-227. Digital Poster Prognostic factors in single-isocenter linac-based SRT for brain metastases: does dose distribution or patient selection matter more? Valeria Faccenda 1 , Denis Panizza 1 , Riccardo Ray Colciago 2 , Sofia Paola Bianchi 3 , Elena De Ponti 1 , Stefano Arcangeli 2 1 Medical Physics, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 2 School of Medicine and Surgery, University of Milan Bicocca, Milan, Italy. 3 Radiation Oncology Department, MedAustron Ion Therapy Center, Wiener Neustadt, Austria Purpose/Objective: The effectiveness of stereotactic radiotherapy (SRT) for brain metastases (BM) is heavily influenced by target dose and patient selection. However, there is limited evidence on which clinical and dosimetric factors best guide Keywords: Glioblastoma, Helical Tomotherapy, Recurrence 117