A control circuit accesses information regarding a given patient. That information may include, for example, segmentation information that depicts at least one treatment volume and at least one organ-at-risk. The control circuit then defines a plurality of dose-calculation sectors for the given patient as a function, at least in part, of the information regarding the given patient. Those dose-calculation sectors are not assumed to be uniformly sized. These teachings can then provide for optimizing a radiation treatment plan, such as a volumetric modulated arc therapy radiation treatment plan, as a function, at least in part, of the plurality of dose-calculation sectors to provide an optimized radiation treatment plan.