Computerized omography (CT), Positron Emission Tomography (PET), and Magnetic Resonance Imaging (MRI) are three distinct ways of imaging a patient. They provide complementary information about the location, physiology and physical properties of the tumor and the surrounding healthy organs.
CT shows bones, which help position the patient. It also provides physical data necessary for the calculation of radiation dose.
Physicians delineate certain types of tumors and some healthy tissues on a CT scan, but sometimes a MRI and/or PET is needed for other types of tumors or organs.
MRI helps with soft tissue visualization, while PET can locate regions where sugar is being preferentially metabolized, such as in tumors.
Using all this information allows one to plan where and how the radiation dose will be delivered.