How is external-beam radiation therapy used to treat colorectal cancer?

External-beam radiation therapy is the type of radiation therapy most often used for people with colorectal cancer. The radiation is focused on the cancer from a machine outside the body called a linear accelerator.

 

Before treatments start, the radiation team takes careful measurements to determine the correct angles for aiming the radiation beams and the proper dose of radiation. External radiation therapy is much like getting an x-ray, but the radiation is more intense. The procedure itself is painless. Each treatment lasts only a few minutes, but the setup time -- getting you into place for treatment -- usually takes longer. Most often, radiation treatments are given 5 days a week for several weeks, but the length of time may be shorter if it is given before surgery.