A method for delivering therapeutic heavy ion radiation to a subject, wherein a therapeutic dose of heavy ions is delivered substantially only to a target volume within the subject by generating a broad field of radiation effect substantially only within the target volume, and wherein the broad field of radiation effect is not generated in non-targeted tissue. The method includes the step of irradiating the target volume with at least two arrays of heavy ion microbeams, wherein the at least two arrays each have at least two parallel, spatially distinct heavy ion microbeams. The two arrays of microbeams are interleaved substantially only within the target volume to form a substantially continuous broad beam of radiation substantially only within the target volume.
