A radiation treatment apparatus, comprising: a ring gantry having a central opening; a radiation treatment head coupled to said ring gantry and rotatable around said central opening in at least a 180 degree arc; wherein said radiation treatment head is mechanically coupled to said ring gantry such that a distance by which the radiation treatment head extends inwardly toward the central opening relative to the ring gantry is dynamically controllable; and a gantry translation apparatus coupled with the ring gantry to translate said ring gantry in a direction of a longitudinal axis extending through said central opening, said radiation treatment apparatus to provide radiation treatment to a target tissue volume of a patient disposed at an isocenter of a treatment vault, the radiation treatment apparatus further comprising: a ring gantry structure within which said ring gantry is housed, said ring gantry structure being translatable along said longitudinal axis between (i) a first location for which the ring gantry structure longitudinally encompasses the isocenter, and (ii) a second location for which the ring gantry structure does not encompass the isocenter; and a 3D imaging device distinct from said ring gantry structure to provide at least one of pre-treatment imaging and setup imaging of the target tissue volume, wherein said 3D imaging device is translatable along said longitudinal axis between (iii) a third location for which the 3D imaging device does not longitudinally encompass the isocenter, and (iv) a fourth location for which the 3D imaging device encompasses the isocenter; wherein both (a) pre-treatment or setup imaging of the target tissue volume by the 3D imaging device, and (b) delivery of radiation treatment to the target tissue volume by the radiation treatment head can be achieved without requiring movement of the patient. a ring gantry having a central opening; a radiation treatment head coupled to said ring gantry and rotatable around said central opening in at least a 180 degree arc; wherein said radiation treatment head is mechanically coupled to said ring gantry such that a distance by which the radiation treatment head extends inwardly toward the central opening relative to the ring gantry is dynamically controllable; and a gantry translation apparatus coupled with the ring gantry to translate said ring gantry in a direction of a longitudinal axis extending through said central opening, said radiation treatment apparatus to provide radiation treatment to a target tissue volume of a patient disposed at an isocenter of a treatment vault, the radiation treatment apparatus further comprising: a ring gantry structure within which said ring gantry is housed, said ring gantry structure being translatable along said longitudinal axis between (i) a first location for which the ring gantry structure longitudinally encompasses the isocenter, and (ii) a second location for which the ring gantry structure does not encompass the isocenter; and a 3D imaging device distinct from said ring gantry structure to provide at least one of pre-treatment imaging and setup imaging of the target tissue volume, wherein said 3D imaging device is translatable along said longitudinal axis between (iii) a third location for which the 3D imaging device does not longitudinally encompass the isocenter, and (iv) a fourth location for which the 3D imaging device encompasses the isocenter; wherein both (a) pre-treatment or setup imaging of the target tissue volume by the 3D imaging device, and (b) delivery of radiation treatment to the target tissue volume by the radiation treatment head can be achieved without requiring movement of the patient. a ring gantry structure within which said ring gantry is housed, said ring gantry structure being translatable along said longitudinal axis between (i) a first location for which the ring gantry structure longitudinally encompasses the isocenter, and (ii) a second location for which the ring gantry structure does not encompass the isocenter; and a 3D imaging device distinct from said ring gantry structure to provide at least one of pre-treatment imaging and setup imaging of the target tissue volume, wherein said 3D imaging device is translatable along said longitudinal axis between (iii) a third location for which the 3D imaging device does not longitudinally encompass the isocenter, and (iv) a fourth location for which the 3D imaging device encompasses the isocenter; wherein both (a) pre-treatment or setup imaging of the target tissue volume by the 3D imaging device, and (b) delivery of radiation treatment to the target tissue volume by the radiation treatment head can be achieved without requiring movement of the patient.