ESTRO 2020 Abstract book

S422 ESTRO 2020

was used for the automated preprocessing and segmentation of clinical 3T T1 scans of 1x1x1 mm 3 resolution. All scans were bias-field inhomogeneity and noise corrected, and automatically segmented. The following structures were segmented and analysed: amygdala, nucleus accumbens, caudate nucleus, hippocampus, globus pallidus, putamen, and thalamus. Structures completely or partially within the GTV volume were censored from analysis. The rate of volume loss was determined with non-parametric permutation tests for volume and dose. Results Significant dose-dependent volume loss was observed in all examined structures, except for caudate nucleus. Rates of volume loss vary from 0.14 to 1.33 % per Gy (corresponding to 4.2% and 39.9% per 30 Gy), and are shown for all structures in Table 1. A 3D representation of the volume loss in some of these structures is shown in Figure 1.

OC-0691 Cerebellar volume reduction after photon or proton radio(chemo)therapy of glioblastoma patients F. RaschkE 1 , A. Seidlitz 1,2,3 , I. Platzek 4 , B. Beuthien- Baumann 5 , J. Van den Hoff 6,7 , D. Krex 8 , J. Kotzerke 7 , C. Jentsch 1,3 , M. Baumann 1,9,10 , M. Krause 1,2,3,11,12 , E. Troost 1,2,3,11,12 1 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 ; 2 German Cancer Consortium DKTK- partner site Dresden, and German Cancer Research Center DKFZ, Dresden, Germany ; 3 Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Department of Radiotherapy and Radiation Oncology, Dresden, Germany ; 4 Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Department of Diagnostic and Interventional Radiology, Dresden, Germany ; 5 German Cancer Research Center DKFZ Heidelberg- Germany, Division of Radiology, Heidelberg, Germany ; 6 Helmholtz- Zentrum Dresden - Rossendorf- Institute of Radiopharmaceutical Cancer Research, Center for Positron Emission Tomography, Dresden-Rossendorf, Germany ; 7 Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Department of Nuclear Medicine, Dresden, Germany ; 8 Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Department of Neurosurgery, Dresden, Germany ; 9 National Center for Tumor Diseases NCT, Partner Site Heidelberg- Germany, Heidelberg, Germany ; 10 German Cancer Research Center DKFZ, Heidelberg- Germany, Heidelberg, Germany ; 11 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- Helmh, ; 12 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology – OncoRay, Dresden-Rossendorf, Germany Purpose or Objective Radio(chemo)therapy is part of the standard treatment of high-grade glioma patients and has been associated with cerebral atrophy 1,2 . Preclinical work also suggests radiation induced atrophy of the cerebellum 3,4 . Investigating cerebellar atrophy in patients treated with radiation is a further step in understanding radiation- induced deficits in both motor function and cognition. The aim of this study was to investigate cerebellar volume changes in a cohort of glioblastoma patients treated with photon or proton radio(chemo)therapy. Material and Methods Data was acquired on a 3T Philips Ingenuity TF PET/MRI scanner (Philips Healthcare, Best, The Netherlands) as part of a prospective, longitudinal study investigating the effect of 11 C-methionine PET/MR for tailoring the treatment of patients with glioblastoma (NCT01873469). In total, 71 patients with cerebral GBM (21 treated with proton therapy) had a baseline MR and at least one follow- up MRI, obtained in 3 monthly intervals after irradiation, available, including 3D T1-weighted (T1w) imaging (1×1×1 mm 3 ) before and after intravenous injection of contrast agent (CE). Patients were treated with a total dose of 60 Gy(RBE=1.1) delivered in 2Gy fractions. On average 3.6 follow-ups were available covering a time period of 413 days ± 432 days (mean ± SD). The cerebellum was cut out from each MRI by warping 5 the MNI152 brain atlas and a corresponding cerebellar mask to

Conclusion We have found that all subcortical deep grey matter structures, with the exception of caudate nucleus, show dose-dependent volume loss after RT. These results challenge us to reconsider the currently used sparing strategies in radiation treatment of brain tumours. Presently, hippocampal sparing RT has been adopted in several institutions. However, sparing the dose in the hippocampus leads to higher doses in surrounding cerebral tissues, which we have shown are also susceptible to radiation-induced damage. Therefore, future research has to focus on the relation between clinical outcomes (like cognitive and motor function) and morphologic changes in the entire brain, not just selected structures. This way we can conclusively say which structures should be avoided in RT planning to prevent radiation-induced damage. Precise sparing of healthy brain is possible with novel techniques like proton therapy and VMAT. This could lead to improved cognition and quality of life in patients undergoing treatment for brain tumours.