Three dimensional conformal radiation therapy, also known as 3D-CRT, uses computers and special imaging techniques to define the shape and size of a tumor. Imaging with computer-assisted tomography (CT or CAT scan), magnetic resonance imaging (MRI) and positron emission tomography (PET) scans are used to define the extent of the disease as well as the critical structures we need to avoid. Our doctors then precisely configure the radiation beams to the size and shape of the tumor.