ESTRO 37 Abstract book

ESTRO 37

S582

both in a qualitative, visual evaluation and in a quantitative evaluation based on the image grey values in a region of interest. The existence of lung fibrosis was confirmed by a histopathological examination of the lungs after sacrificing the mice at the end of the experiment. Additionally, the histopathological examination also revealed local inflammation of the lung, which will be analysed in a follow-up study. Conclusion Dark-field imaging is a useful method for early detection of radiation induced lung fibrosis in mice, as it provides a clearer image of the changes in the murine lung than the corresponding absorption images. Local lung irradiation in mice is a useful model to study normal tissue response and volume effects for the optimization of radiation therapy. PO-1036 Brain modifications after stereotactic radiotherapy recorded by Functional MRI F. Lallemand 1 , N. Leroi 2 , M. Bahri 3 , E. Balteau 3 , A. Noël 2 , P. Coucke 1 , A. Plenevaux 3 , P. Martinive 1 1 C.H.U. - Sart Tilman, Radiothérapie, Liège, Belgium 2 ULg, Laboratory of Tumor and Development Biology, Liège, Belgium 3 ULg, Cyclotron Research Center- University of Liège, Liège, Belgium Purpose or Objective Brain irradiation is commonly used in malignant diseases (i.e. metastases or Glioblastoma) and in benign diseases (i.e. meningioma, epilepsy, vestibular schwannoma or Parkinson disease). The use of stereotactic radiosurgery (SRS) allows the administration of very high doses in a single fraction (e.g. 120Gy), in a small brain volume. After irradiation, morphological and functional cerebral changes occur depending on the total dose, dose per fraction and the irradiated brain volume. The aim of this work is to use f-MRI to record adult normal brain tissue modification after irradiation with different radiotherapy doses and schedules and to identify new parameters of With a dedicated small animal radiotherapy device allowing IGRT (PXI, X-Rad SmART), we specifically irradiated with a 2mm-collimator, mimicking SRS, a small part of adult brain mice (n=72), known to have no impact on vital function, with dose schedules: 1X20Gy, 3X10Gy, 4X5Gy and no RT as control. We imaged brain mice longitudinally with a dedicated 9.4-T MRI (Agilent). Imaging was realized once before as reference level and after irradiation every month for the first 6 months and every 3 months during one year. For each mouse we acquired 14 slices of 1 mm thickness and 0.5 mm gap with an “in plane voxel resolution” of 0.5 mm. We performed T1-weighted, T2-weighted, T1-mapping, T2- mapping and DW-MRI. For DW-MRI, we performed Fast Spin Echo MultiSlice sequences, with 9 different B-value and B0 (from 20 to 1000). We performed IntraVoxel Incoherent Motion (IVIM) analysis to obtain information on intravascular diffusion, related to perfusion ( F : perfusion factor). brain radio-damages. Material and Methods Poster: Radiobiology track: Normal tissue biology of central nervous system

Poster: Radiobiology track: Normal tissue biology of the lung

PO-1035 Detection of radiation induced lung fibrosis using x-ray dark-field imaging in a murine model T. Gora 1 , R. Burkhardt 1,2 , S. Umkehrer 3 , J. Herzen 3 , D. Schilling 1,2 , A. Feuchtinger 4 , A.K. Walch 4 , T.E. Schmid 1,2 , G. Multhoff 1,2 , P.B. Noël 5 , E.J. Rummeny 5 , F. Pfeiffer 3,5,6 , S.E. Combs 1,2 , J.J. Wilkens 1 1 Klinikum rechts der Isar- Technical University of Munich, Department of Radiation Oncology, Munich, Germany 2 Helmholtz Zentrum München, Institute of Innovative Radiotherapy iRT, Neuherberg, Germany 3 Technical University of Munich, Chair of Biomedical Physics- Department of Physics and Munich School of BioEngineering, Garching, Germany 4 Helmholtz Zentrum München, Abteilung Analytische Pathologie, Neuherberg, Germany 5 Klinikum rechts der Isar- Technical University of Munich, Department of Diagnostic and Interventional Radiology, Munich, Germany 6 Technical University of Munich, Institute for Advanced Study, Garching, Germany Purpose or Objective Radiation induced lung fibrosis is a common side effect of radiation therapy and limits the radiation dose that can be applied to treat thoracic tumours. Lung fibrosis leads to an irreversible destruction of the lung, chronic respiratory insufficiency and sometimes death. Usually CT or planar x-rays are employed to detect lung fibrosis; however, these methods are not very sensitive and the differentiation between fibrosis and an early stage of inflammation is difficult. The aim of this study is to test new x-ray dark-field imaging methods to detect radiation induced lung fibrosis in a murine model, and to investigate the influence of different irradiated lung volumes. These insights can help to detect lung fibrosis at an early stage and to optimize treatment planning for humans. Material and Methods 24 C57BL/6 mice were subdivided into four groups to be treated with different irradiation settings: full right lung, upper right lung lobe, lower right lung lobe, all irradiated with 20 Gy in a single fraction, and a control group, which was not irradiated. Local irradiation was performed with 220 kV x-rays using the Small Animal Radiation Research Platform (SARRP, Xstrahl Ltd, UK). Two opposing anterior and posterior oblique fields were used to avoid the heart. Immediately before irradiation and afterwards in regular intervals of four weeks, the mice were imaged for eight months using the novel preclinical imaging device SkyScan 1190 (Bruker, Belgium). It uses x-ray dark-field imaging for both, projection images and CT, and also provides a conventional absorption image (projection and CT), which is later used for comparison. Results First structural changes within the treated area could already be seen 8-12 weeks after irradiation, in most irradiated mice after 20 weeks. These changes increased with time and are clearly visible in the dark-field images. A clear volume effect could be observed, both in terms of severity of the change in lung tissue and in the time of its onset. Therefore, the benefit of dark-field imaging compared to conventional absorption images is apparent