Radiotherapy apparatus for the delivery of an energetic beam to a target tissue in a treatment zone of said radiotherapy system, wherein a) the radiotherapy apparatus comprises a rotatable gantry for rotating the end of a beam delivery system about a circle centered on an isocentre I and normal to an axis of rotation Z1 of the gantry, the path between the end of the beam delivery system and the isocentre I defining a central beam axis Z2 at every rotation angle of the gantry about the axis of rotation Z1; b) the radiotherapy apparatus comprises an imaging ring, said imaging ring comprising a central bore and being defined by a bore axis X1 extending along said central bore, and by a first and a second transverse axis X2, X3 defining an imaging ring plane (X2, X3), said axes X1, X2, X3 being orthogonal and intersecting at a center R of said imaging ring, said imaging ring comprising: i. an imaging system for acquiring images of a patient in an imaging zone of said imaging system, said imaging zone intersecting the bore axis X1; ii. a beamline portion with a channel for the passage of the energetic beam through the imaging ring; c) the imaging ring is located in the radiotherapy apparatus such that its imaging zone intersects the axis of rotation Z1 of the gantry, and the imaging ring is mechanically coupled to the rotatable gantry through a mechanical structure, characterized in that: i. the mechanical structure is mechanically coupled to the gantry in that said mechanical structure is rotatable with respect to the gantry about the central beam axis Z2, and ii. the imaging ring is mechanically coupled to the mechanical structure in that: • the imaging ring center R is located on the the central beam axis Z2 and; • the imaging ring is rotatable with respect to the mechanical structure about a second axis of rotation Y2 of the imaging ring, said axis of rotation Y2 belonging to the the imaging ring plane (X2, X3), said axis of rotation Y2 being perpendicular to said central beam axis Z2. a) the radiotherapy apparatus comprises a rotatable gantry for rotating the end of a beam delivery system about a circle centered on an isocentre I and normal to an axis of rotation Z1 of the gantry, the path between the end of the beam delivery system and the isocentre I defining a central beam axis Z2 at every rotation angle of the gantry about the axis of rotation Z1; b) the radiotherapy apparatus comprises an imaging ring, said imaging ring comprising a central bore and being defined by a bore axis X1 extending along said central bore, and by a first and a second transverse axis X2, X3 defining an imaging ring plane (X2, X3), said axes X1, X2, X3 being orthogonal and intersecting at a center R of said imaging ring, said imaging ring comprising: i. an imaging system for acquiring images of a patient in an imaging zone of said imaging system, said imaging zone intersecting the bore axis X1; ii. a beamline portion with a channel for the passage of the energetic beam through the imaging ring; i. an imaging system for acquiring images of a patient in an imaging zone of said imaging system, said imaging zone intersecting the bore axis X1; ii. a beamline portion with a channel for the passage of the energetic beam through the imaging ring; c) the imaging ring is located in the radiotherapy apparatus such that its imaging zone intersects the axis of rotation Z1 of the gantry, and the imaging ring is mechanically coupled to the rotatable gantry through a mechanical structure, characterized in that: i. the mechanical structure is mechanically coupled to the gantry in that said mechanical structure is rotatable with respect to the gantry about the central beam axis Z2, and ii. the imaging ring is mechanically coupled to the mechanical structure in that: • the imaging ring center R is located on the the central beam axis Z2 and; • the imaging ring is rotatable with respect to the mechanical structure about a second axis of rotation Y2 of the imaging ring, said axis of rotation Y2 belonging to the the imaging ring plane (X2, X3), said axis of rotation Y2 being perpendicular to said central beam axis Z2. i. the mechanical structure is mechanically coupled to the gantry in that said mechanical structure is rotatable with respect to the gantry about the central beam axis Z2, and ii. the imaging ring is mechanically coupled to the mechanical structure in that: • the imaging ring center R is located on the the central beam axis Z2 and; • the imaging ring is rotatable with respect to the mechanical structure about a second axis of rotation Y2 of the imaging ring, said axis of rotation Y2 belonging to the the imaging ring plane (X2, X3), said axis of rotation Y2 being perpendicular to said central beam axis Z2. • the imaging ring center R is located on the the central beam axis Z2 and; • the imaging ring is rotatable with respect to the mechanical structure about a second axis of rotation Y2 of the imaging ring, said axis of rotation Y2 belonging to the the imaging ring plane (X2, X3), said axis of rotation Y2 being perpendicular to said central beam axis Z2.