A high-precision radiotherapy technique, based on the three-dimensional volumetric definition of the tumor and the anatomy of critical organs. A complex process, 3D-CRT begins with creation of individualized, 3D digital data sets of patient tumors and normal adjacent anatomy. These data sets are then used to generate 3D computer images and develop complex plans to deliver highly “conformed” (focused) radiation while sparing normal adjacent tissue. Because higher doses of radiation can be delivered to cancer cells while significantly reducing the amount of radiation received by surrounding healthy tissues, the technique should increase the rate of tumor control while decreasing side effects. 3DCRT is used to treat tumors that in the past might have been considered too close to vital organs and structures for radiation therapy, such as tumors in the head and neck that are close to the spinal cord, optic nerve, salivary glands, and other important structures.