Radiation Therapy for Colon, Rectum and Anus Cancers

External Beam Radiation Therapy

External beam radiation therapy involves a series of daily outpatient treatments to accurately deliver radiation to the area needing treatment. The radiation beam usually comes from a machine called a linear accelerator.

• Before beginning treatment, you will be scheduled for a simulation to map out the area to be treated. This will involve having X-rays and/or a CT scan. Landmarks placed on your skin (often tiny tattoos) allow the radiation therapists delivering your treatments to precisely position you each day.
• To minimize side effects, the treatments are given gradually over about six weeks, five days a week (Monday through Friday). This allows your doctors to get enough radiation into your body to kill the tumor cells while giving healthy cells time to recover each day.
• Technical terms that may be mentioned for colorectal and anal cancer treatments include three-dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT) or image guided radiation therapy (IGRT). Your radiation oncologist can provide more information on these different techniques.
• More about external beam radiation therapy