1. A system for developing a predictive dose-volume relationship for a radiation therapy treatment, the system comprising: a memory area for storing data corresponding to a plurality of patients, the data comprising a three-dimensional representation of the planning target volume and one or more organs-at-risk, the data further comprising an amount of radiation delivered to the planning target volume and the one or more organs-at-risk; and one or more processors programmed to: access, from the memory area, the data corresponding to to the plurality of patients, the data comprising a three-dimensional representation of the planning target volume and one or more organs-at-risk, the data further comprising an amount of radiation delivered to the planning target volume and the one or more organs-at-risk; and develop a model that predicts dose-volume relationships using the three-dimensional representations of the planning target volume and the one or more organs-at-risk, the model being derived from correlations between dose-volume relationships and calculated minimum distance vectors between discrete volume elements of the one or more organs-at-risk and a boundary surface of the planning target volume.