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Radiation Oncology - Page 2

© David Olle

a. Three dimensional conformal radiation therapy is used to target a tumor more precisely with radiation beams. A 3-D image of a tumor can be obtained using computed tomography, magnetic resonance imaging, positron emission tomography, or single photon emission computed tomography. Using information from the image, special computer programs design radiation beams that conform to the shape of the tumor. Since healthy tissue is spared from the radiation, higher doses can be used to treat the cancer. b. Intensity-modulated radiation therapy uses radiation beams of varying intensity to deliver different doses of radiation to small areas of tissue at the same time. This technique allows greater doses of radiation to be delivered within the tumor. c. Stereotactic radiosurgery 1 applies a single large dose of radiation to a small tumor. It has found application for brain tumors. Since the targeting is very precise, the patient's head is fixed in a frame during treatment. Stereotactic radiotherapy is more applicable for organs that move. The procedure delivers multiple smaller doses of radiation, and uses a non-fixed frame.

2. Internal radiation therapy applies radiation very close or inside the tumor. The radiation source (a radioactive isotope, known as a redionuclide) is sealed in an implant in such forms as wires, tubes, capsules, or seeds. The isotope chosen has a short half-life, so that radiation dissipates over a relatively short time. 3. Systemic radiation therapy uses unsealed radioactive materials that travel throughout the body. This technique is necessary for cancers that are widespread, such as non-Hodgkin's lymphoma. A recent advance in this field is the use of radiolabeled antibodies. The technique begins with the identification of specific antigens on the tumor surface for which large quantities of antibodies can be prepared in the laboratory. A radionuclide is then attached to the antibodies, and the preparation injected into the patient. The antibodies seek out the cancer cells, attach to them, and the radiation kills the cells.

How can the effect of radiation be modified? 4

Radiosensitizers are drugs that make cancer cells more sensitive to the effects of radiation therapy. Additionally, some anticancer drugs, such as 5-fluorouracil and cisplatin, make cancer cells more sensitive to radiation therapy.

Radioprotectors are drugs that protect non-cancerous cells from the damage caused by radiation therapy. Amifostine is an example.

What are some of the hazards to radiation therapy? 3

Since radiation therapy exerts its greatest effect on fast growing tissue, any normal tissue in the body that has a rapid turnover can be affected. This can include the male testes, female ovary, bone marrow, skin, mucosal lining of the intestinal tract, and the epithelial lining of the blood vessels. Other organs can be affected. These effects can be either acute or long lasting.

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