The present invention relates to a method of controlling a medical apparatus (100), the method comprising receiving location data indicative of the location of a target volume (146); controlling a positioning system (224) to rotate a therapy device comprising an energy-delivering device about a longitudinal axis of the therapy device; controlling the energy-delivering device to deliver energy to the target volume (146) at a first rotation position relative to the longitudinal axis on a rotation trajectory of the therapy device using the location data; determining a first set of slice planes of the target volume (146) at the first rotation position to be imaged by a magnetic resonance imaging module (106); controlling the magnetic resonance imaging module (106) to acquire first magnetic resonance data from the first set of slice planes of first set of slice planes; determining a second set of slice planes of the target volume (146) at least one second rotation position of the therapy device on the rotation trajectory to be imaged by the magnetic resonance imaging module (106); and controlling the magnetic resonance imaging module (106) to acquire second magnetic resonance data from the second set of slice planes.