External radiation therapy, or teletherapy, uses a beam of radiation directed at the tumor. Once the area of cancer is identified, a small ink tattoo is fixed on the skin over the area of cancer so that the radiation beam can be focused on the same spot for each treatment. It is necessary to focus the radiation beam on the cancer cells and to shield nearby healthy tissue from the radiation. External radiation therapy is usually done in multiple treatments, usually once a day for several weeks.
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