Radiation therapy uses x-rays to kill cancer cells that might remain after an operation or to shrink large tumors before an operation so that they can be removed surgically. The object of radiation therapy is to damage the tumor as much as possible without harming surrounding tissues. Radiation may be administered in one of the following two ways:
- Externally from a source outside the body, such as a linear accelerator (external beam radiation)
- Internally through small radioactive pellets implanted directly into the tumor (brachytherapy)
Preoperative and Postoperative Radiation with Chemotherapy
The main use for radiation therapy in people with colon cancer is when the cancer has attached to an internal organ or the lining of the abdomen. When this occurs, the surgeon cannot be certain that all the cancer has been removed, and radiation therapy may be used to kill any cancer cells remaining after surgery. Radiation therapy is seldom used to treat metastatic colon cancer because of side effects, which limit the dose that can be used.
For rectal cancer, radiation therapy is usually given to help prevent the cancer from coming back in the pelvis where the tumor started. It may be given either before or after surgery, but recently doctors have begun to favor preoperative treatment, along with chemotherapy. If a rectal cancer's size or position make surgery difficult, radiation may be used before surgery to shrink the tumor. Radiation therapy can also be given to help control rectal cancers in people who are not healthy enough for surgery.
Radiation also may be used to ease (palliate) symptoms in people with advanced cancer causing intestinal blockage, bleeding, or pain.
Review Date: 10/21/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.