Integration of magnetic resonance imaging (MRI) in proton therapy (PT) has the potential to improve tumor-targeting precision. However, it is technically challenging to integrate an MRI scanner at the beam isocenter of a PT system due to space constraints and electromagnetic interactions between the two systems. We present a concept for the mechanical integration of a 0.5 T MRI scanner (MR-Open, ASG Superconductors) into a PT gantry (ProteusONE, IBA). Finite element modelling (FEM) simulations are used to assess the perturbation of several of the gantry's elements on the homogeneity of the scanner's static magnetic field. Results show that only the perturbations by the bending magnet are significant and to be taken into account during treatment planning and dose delivery.