IOP PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 53 (2008) 3609–3622 doi:10.1088/0031-9155/53/13/015 Brain tumor vessel response to synchrotron microbeam radiation therapy: a short-term in vivo study Rapha¨ el Serduc 1,2,5 , Thomas Christen 1,2 , Jean Laissue 3 , R´ egine Farion 1,2 , Audrey Bouchet 1,2 , Boudewijn van der Sanden 1,2 , Christoph Segebarth 1,2 , Elke Br¨ auer-Krisch 4 , G´ eraldine Le Duc 4 , Alberto Bravin 4 , Chantal R´ emy 1,2 and Emmanuel L Barbier 1,2 1 INSERM, U836, F38043 Grenoble, France 2 Universit´ e Joseph Fourier, Grenoble Institut des Neurosciences, F38043 Grenoble, France 3 Institute of Pathology, University of Bern, Switzerland 4 European Synchrotron Radiation Facility, F38043 Grenoble, France E-mail: serduc@esrf.fr Received 16 December 2007, in final form 7 May 2008 Published 17 June 2008 Online at stacks.iop.org/PMB/53/3609 Abstract The aim of this work focuses on the description of the short-term response of a 9L brain tumor model and its vasculature to microbeam radiation therapy (MRT) using magnetic resonance imaging (MRI). Rat 9L gliosarcomas implanted in nude mice brains were irradiated by MRT 13 days after tumor inoculation using two orthogonal arrays of equally spaced 28 planar microbeams (25 µm width, 211 µm spacing and dose 500 Gy). At 1, 7 and 14 days after MRT, apparent diffusion coefficient, blood volume and vessel size index were mapped by MRI. Mean survival time after tumor inoculation increased significantly between MRT-treated and untreated groups (23 and 28 days respectively, log-rank test, p < 0.0001). A significant increase of apparent diffusion coefficient was observed 24 h after MRT in irradiated tumors versus non-irradiated ones. In the untreated group, both tumor size and vessel size index increased significantly (from 7.6 ± 2.2 to 19.2 ± 4.0 mm 2 and +23%, respectively) between the 14th and the 21st day after tumor cell inoculation. During the same period, in the MRT-treated group, no difference in tumor size was observed. The vessel size index measured in the MRT-treated group increased significantly (+26%) between 14 and 28 days of tumor growth. We did not observe the significant difference in blood volume between the MRT- treated and untreated groups. MRT slows 9L tumor growth in a mouse brain but MRI results suggest that the increase in survival time after our MRT approach may be rather due to a cytoreduction than to early direct effects of ionizing 5 Present address: Centre de Recherche Cerveau et Cognition, UMR5549 CNRS-Universit´ e Toulouse. Visiting Scientist, European Synchrotron Radiation Facility, 6 rue Horowitz, F38043 Grenoble, France. 0031-9155/08/133609+14$30.00 © 2008 Institute of Physics and Engineering in Medicine Printed in the UK 3609