In a method and system for planning and implementing a selective internal radiation therapy (SIRT), the liver volume and the tumor volume are automatically calculated in a processor by analysis of items segmented from images obtained from the patient using one or more imaging modalities, with the administration of a contrast agent. The volume of therapeutic agent that is necessary to treat the tumor is automatically calculated from the liver volume, the tumor volume, and the body surface area of the patient and the lung shunt percentage for the patient. The therapeutic agent can be administered via respective feeder vessels in respectively different amounts that correspond to the percentage of blood supply to the tumor from the respective feeder vessels, this distribution also being automatically calculated by analysis of one or more parenchymal blood volume (PBV) images.