A patient positioning device for use in simulation and treatment via radiation therapy of the ipsilateral breast of a patient while in the prone position. The patient positioning device has (A) an MRI coil support system comprising (a) at least one of (1) a first MRI coil support structure at the superior end of the device, and (2) a second MRI coil support structure at the inferior end of the device, wherein the first and/or second support structures are dimensioned and configured to receive and engage a first MRI coil at one or more positions and oriented in the vertical plane, and (b) an MRI support assembly comprising a housing dimensioned and configured to receive and engage a second MRI coil, wherein the MRI support assembly is configured to allow adjustment of the position of the housing relative to the one or more positions for receiving and engaging the first MRI coil, (B) an aperture through which the ipsilateral breast can hang into a radiation therapy treatment field, and (C) a provision to support the contralateral breast such that it is held out of the radiation therapy treatment field. Both the first and second MRI coils are positioned such that neither comes in physical contact with the ipsilateral breast.Linvention concerne un dispositif de positionnement de patient destiné à être utilisé dans une simulation et un traitement par thérapie par rayonnement du sein ipsilatéral dun patient dans la position allongée. Le dispositif de positionnement de patient comprend (A) un système de support de bobine dIRM comprenant (a) au moins lune parmi (1) une première structure de support de bobine dIRM sur lextrémité supérieure du dispositif et (2) une seconde structure de support de bobine dIRM sur lextrémité inférieure du dispositif, les première et/ou seconde structures de support étant dimensionnées et configurées pour recevoir et accoupler une première bobine dIRM dans une ou plusieurs positions et orientées dans le plan vertical, et (b) un ensemble support
