ESTRO 2023 - Abstract Book

S541

Sunday 14 May 2023

ESTRO 2023

received long-course hRT. Patients treated with SC had a 2-year OS of 29.3%, whereas patients treated with long course hRT had a 2-year OS of 35.2%. Multivariate Cox regression, which took into account varying total dosages and age, revealed an association between age and overall survival (OS), with OS falling in patients older than 62 years (hazard ratio [HR], 1.82, p<0.001, IC 95%: 1.33-2.50). Conclusion Long-course hRT seems to have comparable survival rates as standard fractionation in a large real-world series of GBM patients, but with the benefit of a slight reduction in overall treatment time. PD-0651 Diffusion changes in normal-appearing white matter tracts following irradiation in glioma patients K. Witzmann 1,2 , F. Raschke 1,2 , T. Wesemann 3 , H. Wahl 3 , S. Appold 4 , M. Krause 1,2,4,5,6 , J. Linn 3 , E.G.C. Troost 1,2,4,5,6 1 Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiooncology – OncoRay, Dresden, Germany; 2 OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany; 3 Institute of Neuroradiology, University Hospital Carl Gustav Carus and Medical Faculty of Technische Universität, Dresden, Germany; 4 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; 5 German Cancer Consortium (DKTK), Partner Site Dresden, and German Cancer Research Center (DKFZ), Heidelberg, Germany; 6 National Center for Tumor Diseases (NCT), Partner Site Dresden, Germany: German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany, and; Helmholtz Association / Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany Purpose or Objective Adjuvant radio(chemo)therapy (RT) is part of the standard treatment of gliomas. Safety margins ensuring the coverage of microscopic tumour expansion of diffusely infiltrating gliomas and compensating for systematic positioning errors inevitably result in the normal-appearing (NA) brain tissue surrounding the tumour to be affected by radiation. The aim of the study was to investigate dose- and time-dependent diffusion alterations of NA white matter (WM) structures following RT using tract-based spatial statistics (TBSS). Materials and Methods As part of a prospective, longitudinal study, magnetic resonance imaging (MRI) data of 24 grade II-IV glioma patients treated with photons, protons or mixed-modality therapy were acquired. MRIs before RT and 3-monthly during follow-up obtained up to three years after RT included diffusion tensor images (DTI) (TR/TE=6500/66ms, 2 × 2 × 2mm ³ , 32 directions, b=1000mm/s ² ). Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated from the DTI data. Corresponding radiation dose maps and clinical target volume (CTV) contours were aligned to MRI using ANTs. NA tissue was defined as brain tissue, excluding the CTV and areas of T2-hyperintensities. All FA images were nonlinearly registered to the “FMRI58B-FA atlas” from FSL with ANTs before applying parts of the TBSS algorithm to create a FA skeleton (Figure 1). The FA skeleton was combined with the “JHU-ICBM-labels-1mm atlas” to measure the diffusion in 19 WM structures. Relative signal changes of each WM structure were calculated as the difference between follow-up and the corresponding baseline signal and evaluated using a paired t-test. A multivariate linear mixed effects model was applied to determine diffusion changes as function of time after RT and mean dose delivered to the corresponding structure. Data from paired structures of the right and left hemispheres were combined for the analysis. Structures containing less than 50 voxels were excluded. PD-0650 The prediction radiomics model of pseudoprogression in glioblastoma Abstract withdrawn