A computed tomography (CT) scan, also called a Cat Scan, is a diagnostic exam used to detect tumors, determine the stage of the disease and whether cancerous cells have spread, and find out about the effectiveness of cancer treatment. CT scans are also used to guide some types of biopsies (the removal of a small amount of tissue for examination to determine whether cancer is present). Common areas that may be scanned include the head, neck, chest, abdomen, pelvis, or an extremity. The CT scanner takes a series of x-ray pictures, which are combined by a computer to create extremely detailed, cross-sectional images of your internal organs or other parts of your body that cannot be examined with conventional x-rays. CT is used to detect or confirm the presence of a tumor; to provide information about the size and location of the tumor and whether it has spread, to help plan radiation therapy or surgery; and to determine whether the cancer is responding to treatment.