1. A method executed on a computing device, the method for estimating a dose and developing a radiation therapy plan, the method comprising: executing, with a processor of the computing device, a dose distribution planning tool stored as programming code in a computer-readable medium of the computing device, wherein said executing comprises: subdividing a representation of a volume of interest into a first plurality of voxels; determining a first distance between an origin of a first planned radiation field of a radiation beam and a first voxel of the first plurality of voxels that is traversed by the first planned radiation field; computing a first metric based on the first distance, a prescription dose associated with a target volume outside the volume of interest, and a first field parameter; and evaluating the first metric and determining a beam orientation for delivering the prescription dose to the target volume, wherein said determining a beam orientation comprises including the first planned radiation field in the radiation therapy plan if the first metric satisfies a dose constraint for the volume of interest.