1. A radiation system for developing a predictive dose-volume relationship for a radiation therapy treatment, the system comprising: a radiation data memory device for storing data corresponding to a plurality of patients, the data comprising a three-dimensional representation of a 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; a display device; and one or more radiation data processors programmed to: access, from the radiation data memory device, the data corresponding to the plurality of patients; 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 from the data corresponding to the plurality of patients, wherein the model is developed by: calculating a dose-volume relationship corresponding to the irradiation of the planning target volume for each patient of the plurality of patients; calculating a set of minimum distance vectors between discrete volume elements of the one or more organs-at-risk and a boundary surface of the planning target volume; and determining a correlation between the calculated dose-volume relationship and the calculated set of minimum distance vectors between the one or more organs-at-risk to the boundary surface of the planning target volume using a probability distribution function to fit the set of minimum distance vectors; receive data corresponding to a three-dimensional representation of the planning target volume and the one or more organs-at-risk of a new patient; calculate minimum distance vectors between discrete volume elements of the one or more organs-at-risk of the new patient and a boundary surface of the planning target volume of the new patient; predict dose-volume relationships for the planning target volume and the one or more organs-at-risk of the new patient using the developed model and the calculated minimum distance vectors for the new patient; and treat the new patient based at least in part on the predicted dose-volume relationships for the planning target volume and the one or more organs-at-risk of the new patient.