An in-line MRI-linac apparatus is provided that includes an MRI magnet of an MRI scanner, where the MRI magnet generates a magnetic field, where the magnetic field has a quasi-uniform fringe field, where the fringe field is proximal to an axis of symmetry of the MRI magnet, and a magnetically unshielded dynamically moveable linac that includes a treatment beam that is aligned with field lines of the fringe field in a quasi axial symmetric configuration, where a position of the linac in the fringe field continuously adapts according to a target position to enable continuous dose delivery to the target.
