1. A five degree-of-freedom gantry positioning apparatus for a radiation imaging system, the gantry positioning apparatus adapted to connect a gantry to a support structure, comprising: a first linear positioner for translating a gantry in a first direction relative to the support structure; a second linear positioner for translating the gantry in a second direction relative to the support structure, the second direction being orthogonal to the first direction; a third linear positioner for translating the gantry in a third direction relative to the support structure, the third direction being orthogonal to the first and second directions; a first rotary positioner for rotating the gantry about a first axis relative to the support structure; and a second rotary positioner for rotating the gantry about a second axis relative to the support structure.