Radiotherapy apparatus comprising an imaging ring

A radiotherapy apparatus for the delivery of an energetic beam to a target tissue in a treatment zone, including: a rotatable gantry for rotating the end of a beam delivery system about a circle centered on an isocentre and normal to an axis of rotation Z1 of the gantry, the path between the end of the beam delivery system and the isocentre defining a central beam axis Z2 at every rotation angle of the gantry about the axis of rotation Z1; an imaging ring having a central bore and an imaging system for acquiring images of a patient in an imaging zone of the imaging system, wherein the imaging ring is located in the radiotherapy apparatus such that its imaging zone intersects the axis of rotation Z1 of the gantry, and wherein the imaging ring is mechanically coupled to the rotatable gantry through a mechanical structure.