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How It's Done

External beam radiation therapy

Before external radiation therapy begins, a radiation oncologist will plan your treatments. He or she will determine the dose of radiation, how it will be delivered, and the number of treatment sessions.

You will participate in a simulation session to help the radiation oncologist plan the treatment. He or she might mark your skin with tiny permanent or semi-permanent tattoos. This helps ensure that the radiation hits the same spot every time. Alternatively, he or she may implant tiny gold seeds in your body. Called gold fiducials, they mark the edges of the area to be treated; they are viewed with imaging equipment at the start of each therapy session. Doing so makes focusing the radiation beam as accurate as possible from one treatment session to the next. It also lowers the risk that radiation will strike and damage normal tissue. For some cancers in the pelvis, having a full bladder helps focus the radiation beam.

Depending on the body area to be treated, you might need to remove your clothing and put on a hospital gown. In the radiation therapy room, you will lie on a table or sit in a special chair.

The therapist will check the marks on your skin (or the location of the fiducials) to find the exact treatment area. Special blocks or shields will protect other parts of your body. You need to be in the same position and remain still during every treatment so that the radiation hits its target. That's why a mold may be made of part of your body; you will be placed in the mold for treatment.

After you are positioned, the radiation oncologist will go to a control room nearby. From there, he or she will operate the treatment machine while watching you on a monitor or through a window. You might hear the machine make buzzing noises, and it might rotate around you.

Treatments typically are painless and brief, lasting one to five minutes. Your total time in the treatment room will be about five to 15 minutes. Usually, treatments will be given every weekday for several weeks. The weekend break gives normal cells affected by radiation some time to recover.

The type of radiation you receive and how it's delivered can vary from one center to another. Nearly all centers use some type of three-dimensional planning, called three-dimensional conformal radiation therapy, or 3D-CRT. Radiation oncologists and physicists determine the angles at which the radiation beams should enter the tissue. In this way, the radiation field conforms to the shape of the area to be treated.

Intensity-modulated radiation therapy (IMRT) is a form of 3D-CRT. It allows doctors to change the intensity of the radiation within each of the radiation beams. This increases the amount of radiation delivered to the tumor. It also helps spare healthy tissue.

Proton beam therapy uses beams of protons instead of x-rays. Proton therapy may be recommended for treating certain parts of the body, such as the eyes, face, skull, and spine.

Another device, called CyberKnife, accurately delivers very high doses of radiation. This shortens the total time needed for therapy. For example, traditional radiation therapy may last six to eight weeks. With CyberKnife, treatment may last just a few days.

Internal radiation therapy

If you are having internal radiation therapy, your treatment will be different. One type of internal radiation therapy is brachytherapy. (It's also called interstitial radiation therapy or "seed" therapy.) If you have this procedure, you will be given anesthesia. Radioactive seeds will be implanted directly into the tumor or a nearby area. The seeds will remain in your body permanently or be removed after a period of time, depending on the cancer.

Another type, called intracavitary therapy, involves placing radioactive material directly inside a body cavity, such as the uterus, vagina, or rectum. The radioactive material will be removed after a period of time.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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