Patent ID: 8836332

Claim:
A radiation therapy system, comprising: a magnetic resonance imaging (MRI) system, the MRI system including first and second main MRI magnets separated by an MRI magnet gap, wherein the first and second main MRI magnets operate together in order to produce a magnetic field, at least a portion of the magnetic field extending along a first longitudinal axis that extends through an isocenter of the first and second main MRI magnets; a gantry positioned in the MRI magnet gap, the gantry being rotatable about the first longitudinal axis; a linear particle accelerator (linac) supported by the gantry at a first fixed radial distance from the isocenter of the first and second main MRI magnets, the linac being aligned along a second longitudinal axis and being configured to rotate with the gantry and configured to direct a radiation beam towards the isocenter of the first and second main MRI magnets; and a magnetic shield supported by the gantry at a second fixed radial distance from the isocenter of the first and second main MRI magnets, wherein the magnetic shield includes at least a first shell and a second shell, the first shell at least partially surrounding both the linac and the second shell, and wherein at least one of the first shell and the second shell is formed of a material that includes steel.