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What is Radiation Therapy? Print E-mail
Written by Amanda Wattson, MD   
Wednesday, 11 November 2009

Radiation therapy involves the use of radioactive waves to treat certain types of cancer. The therapy can be given with external beams of radiation or brachytherapy. External-beam radiation directs radioactive waves at targeted portions of the body. Brachytherapy involves an implant of radioactive material inside the body.

Radiation affects molecules, proteins, and DNA in cells. The cells become damaged and are unable to function and divide normally. Cancer cells are more susceptible to radiation because they can't repair the damage. Some cancers are considered "radiosensitive" and curable with radiation. Other cancers are resistant to radiation.

Who is a candidate for the procedure?
Because it works so well, radiation is now used in at least half of all individuals with cancer. Many cancers can be cured solely with radiation therapy. These include:
_ cancer of the cervix
_ cancer of the larynx
_ germ cell cancer
_ Hodgkin's lymphoma
_ prostate cancer

Other cancers are treated with radiation to improve symptoms, not to cure the person. These include:
_ breast cancer
_ colorectal cancer
_ lung cancer
_ melanoma, which is a skin cancer

The decision to use radiation therapy, and how to use it, depends on a number of factors. Among them are the tissue type and the location and stage of the cancer. The healthcare provider will also consider the person's overall state of health.

Low-energy radiation is also used for a few noncancerous conditions, such as a skin disease known as psoriasis. Total body radiation at low doses is used before bone marrow transplants. It destroys the existing bone marrow and suppresses the immune system.

How is the procedure performed?
Radioactive implants can be placed anywhere inside the body. Implants may use wires or rods that are placed at the site of the tumor. They may contain radioactive cesium, radium, or iridium. The implants can remain in place for several hours to several days. They are removed after the dose of radiation has been delivered. They do not hurt and are not generally noticeable once they are in the body.

Electron beams are low energy. They are often used for skin conditions and cancers. High-energy particles can penetrate deeply and are used for brain or deep solid tumors. Higher doses of radiation are used for radiation-resistant cancers and when there is an intent to cure. Lower doses are used for radiosensitive cancers and to relieve symptoms.

Any form of radiation can be combined with chemotherapy. This combination therapy has more benefits and more side effects. Fluorouracil (5-FU), doxorubicin, hydroxyurea, and cisplatin are examples of radiosensitizing chemotherapy medicines. They make the targeted tissue more susceptible to radiation therapy.

Another form of radiation therapy is radioactive iodine. It is swallowed as a liquid and circulates through the body. It is used to treat thyroid cancer. The radioactivity disappears within a few weeks.

The procedure to deliver external-beam radiation is somewhat similar to giving an X-ray. The person is put into position, and the machine delivers the radiation to the desired area. External-beam therapy involves cobalt and protons or electrons. It is given over several minutes, usually once a day for several weeks. The higher the energy, the deeper into the body the radiation can go.


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