1. A method for determining a radiation therapy dose distribution, the method comprising: determining an organ at risk (OAR) distance to target map, wherein the OAR distance to target map comprises distances to a target organ for respective portions of at least one OAR as determined from at least one segmented patient organ image; selecting a cohort average dose distance to target histogram from a database; and assigning a dose value to each of the portions of the at least one OAR to form a first 3D dose distribution map, wherein the assigned dose values are derived from the selected cohort average dose distance to target histogram.