an apparatus for supporting an x - ray source in a space having at least one wall and used for exposing patients to x - ray radiation , the apparatus comprising : an upright support member mountable adjacent to the wall ; a slidably movable carriage supported by the support member and slidable thereto for planar movement in a plane parallel to the wall ; a source assembly mounted to the slidable carriage , and adapted to receive the x - ray source , the source assembly including : a horizontally projecting base member fixed to the carriage ; a horizontally extending tubular member pivotally mounted to the base member for pivotal motion in a horizontal plane ; a stem receivably journalled within the tubular member for horizontal reciprocation with respect thereto ; and a source attachment fixed to the source and including a collar journalled around the stem to provide rotational movement in a vertical plane about the stem .