a system and method of radiation planning . the system and method are configured to implement or include the steps of obtaining an image of a patient encompassing tumorous and non - tumorous tissue , applying an encompassing field to the image having an area covering the tumorous and non - tumorous tissue , using a graphical user interface to subtract subset fields from the encompassing field corresponding to radiation sensitive non - tumorous tissues to define a treatment area , and inputting the treatment area to a computer program to generate a radiation treatment plan based on at least one prescribed dose to the treatment area .