Modern CT machines take continuous pictures in a helical (or spiral) fashion rather than taking a series of pictures of individual slices of the body, as the original CT machines did. Helical CT (also called spiral CT) has several advantages over older CT techniques: it is faster and produces better quality 3-D pictures of areas inside the body, which may improve detection of small abnormalities.

CT has many uses in the diagnosis, treatment, and monitoring of cancer, including

• screening for cancer
• helping diagnose the presence of a tumor
• providing information about the stage of a cancer
• determining exactly where to perform (i.e., guide) a biopsy procedure
• guiding certain local treatments, such as cryotherapy, radiofrequency ablation, and the implantation of radioactive seeds for brachytherapy
• helping plan external-beam radiation therapy or surgery
• determining whether a cancer is responding to treatment
• detecting recurrence of a tumor