A method for determining a radiation treatment plan for a patient includes determining a reference plan, the reference plan including information regarding a reference region that has a different configuration from that of a region in the patient, and using the reference plan to determine the treatment plan for the patient. A method for use in a treatment planning process includes determining a reference plan that includes information regarding a reference region, determining a deformation field that registers the reference region in the reference plan with a region for a patient, and determining a result of using the reference plan as it applies for the patient.
