A system and method is provided for radiation system collimation and design. A plurality of channel waveguide assemblies are provided to be operatively associated with respective beam collimators having varying longitudinal bore diameters. The plurality of channel waveguide assemblies includes a plurality of guides and concentric spacers. The plurality of guides and concentric spacers include varying inner diameters that are configured to be securably nested together by decreasing inner diameters and secured within the longitudinal bores of the respective beam collimators.