A magnetic resonance imaging (MRI) and radiation therapy system is described. The system comprises a magnet gantry, an MRI apparatus, a patient support system and a radiation source head. The magnet gantry is configured to rotate about a magnet gantry axis. The MRI apparatus is coupled to the magnet gantry. The radiation source head is coupled to the MRI apparatus via a radiation source arm. The radiation source head is configured to emit a treatment beam at varying angles with respect to an azimuthal gantry axis. A method for performing stereotactic radiosurgery (SRS) using a magnetic resonance (MR)-SRS is also described.
