A method for determining a radiation therapy dose distribution includes selecting a treatment type from a database. An organ at risk (OAR) distance to target map is determined. The OAR distance to target map includes distances to a target organ for respective portions of an OAR, and the OAR distances are determined from a segmented patient organ image. A cohort average dose distance to target histogram is selected from the database. Dose values to the portions of the OAR are assigned to form a first 3D dose distribution map, where the dose values are from the selected cohort average dose distance to target histogram. A second 3D dose distribution map is determined based on a field arrangement determined by the treatment type, and the first 3D dose distribution map. A dose distance to target histogram is calculated using the second 3D dose distribution map and the distance to target map.