QLTI-21. Flattening Filter-Free Beams in Medulloblastoma Radiotherapy: A Comprehensive Dosimetric Analysis

Abstract BACKGROUND Medulloblastoma is an aggressive pediatric brain tumor requiring precise radiotherapy. Cranio-spinal irradiation (CSI) presents challenges in dose delivery, with potential long-term side effects. This study investigates the dosimetric impact of flattening filter-free (FFF) beam technology compared to conventional radiotherapy techniques. METHODS A retrospective analysis of 10 medulloblastoma patients treated between January 2019 and January 2022 was conducted. Three radiotherapy techniques were evaluated: 3D Conformal Radiotherapy (3DCRT), Intensity-Modulated Radiotherapy (IMRT), and RapidArc Therapy. Statistical analysis included paired t-tests and ANOVA, with significance set at p<0.05. Dosimetric parameters were compared using:•Conformity Index (CI) •Dose-Volume Histograms (DVHs) •Dose homogeneity indices •Organ at Risk (OAR) dose measurements RESULTS •PTV D98% showed no clinically significant difference (FF: 2282.4 ± 123.5 cGy vs. FFF: 2283.8 ± 139.8 cGy, p=0.028) •Hippocampus maximum dose significantly lower in FFF mode (1470.2 ± 136.3 cGy vs. 1612.9 ± 175.3 cGy, p<0.001) •Monitor Units higher in FFF mode (1955.8 ± 198.6 vs. 1641.9 ± 177.2, p<0.001) •Conformity Index slightly improved in FFF mode (0.884 ± 0.015 vs. 0.876 ± 0.015, p=0.001) CONCLUSION FFF beam technology offers subtle dosimetric advantages, particularly in reducing dose to critical structures like the hippocampus, while maintaining comparable target coverage. The technique shows promise in improving radiotherapy precision for medulloblastoma patients, potentially minimising long-term radiation-induced side effects.