Intratreatment FDG-PET During Radiation Therapy for Gynecologic and Gastrointestinal Cancers

At radiation planning subjects will have a PET-CT. The CT scan - also called computerized tomography or just CT - combines a series of X-ray views taken from many different angles to produce cross-sectional images of the bones and soft tissues inside the body. CT scans in planning radiation therapy are standard of care. A PET is a highly specialized imaging technique that uses short-lived radioactive substances (such as FDG a simple sugar labeled with a radioactive atom) to produce three-dimensional colored images of those substances functioning within the body. These images are called PET scans and the technique is termed PET scanning. PET scanning provides information about the body's chemistry not available through other procedures. Unlike CT or MRI (magnetic resonance imaging), techniques that look at anatomy or body form, PET studies metabolic activity or body function.