P13.05.B DYNAMICS OF POST-RADIOTHERAPY MORPHOLOGICAL CHANGES IN THE BRAIN

Abstract BACKGROUND Radiotherapy is essential in achieving local control for many brain tumours. However, it carries the risks of toxicities, including neuro-cognitive decline, with potential impact on quality of life. Several brain areas and structures are involved in cognition, but their radiosensitivity and clinical response to radiotherapy is not yet fully understood, and no dose-thresholds are yet established. We studied the dynamics of morphological changes on MRI imaging of 18 brain structures following radiotherapy and investigated predictive factors of their occurrence. Identifying such imaging biomarkers could help develop sparing strategies and improve treatment planning. MATERIAL AND METHODS We included 40 patients treated for gliomas in a tertiary cancer center between 2018-2022 and contoured a set of 18 structures on T1-MRI sequences acquired at 3, 6, 9 months, 1 and 2 years after treatment. Dosimetric data were extracted from dose-volume histograms of the delivered plan, and for each structure the baseline volume and volumes in dynamics were noted. Correlations were tested by calculating the Spearman coefficient (rho) and comparisons between different groups were made using the paired Wilcoxon test, with statistical significance for p2.67Gy/fr). Most structures registered a slight increase in volume at 3 months, followed by a gradual decrease over the two-year follow-up A correlation was observed between the dynamics of Hippocampal and Putamen volumes with Dmean, with loss of 0.55% of Hippocampal volume with each additional 1 Gy added to Dmean (rho = -0.293, p = 0.054) and 0.45% decrease in Putamen volume for every additional 1 Gy for Dmean (rho = -0.373, p = 0.018). The magnitude of volumetric changes was not significantly associated with dose per fraction, patient age, or overall treatment time. CONCLUSION In our cohort of patients, we identified a particular pattern of post-irradiation volume dynamics in selected structures, with a slight increase in volume as an acute effect, followed by progressive, dose-dependent, late atrophy. Our results pave the way for further exploration and validation in subsequent studies, including