Internal radiation therapy is a form of treatment where a source of radiation is put inside your body. One form of internal radiation therapy is called brachytherapy. In brachytherapy, the radiation source is a solid in the form of seeds, ribbons, or capsules, which are placed in your body in or near the cancer cells. This allows treatment with a high dose of radiation to a smaller part of your body. Internal radiation can also be in a liquid form. You receive liquid radiation by drinking it, by swallowing a pill, or through an IV. Liquid radiation travels throughout your body, seeking out and killing cancer cells.
Radioactive isotopes used in brachytherapy: The radioactive isotopes in brachytherapy are as follows:
Radium – 226
Cesium – 137
Gold – 198
Radon – 222
Brachytherapy sources are applied in three ways: external applicators or molds, interstitial implantation, and intracavitary therapy (fig a). A choice of one technique or the other is dictated primarily by the size and location of the tumor. For example, surface molds are used to treat small superficial areas, such as the ear or the lip; interstitial therapy is indicated when the tumor is well localized and can be implanted directly according to accepted rules of distribution; intracavitary therapy is used when applicators containing radioactive sources can be introduced into body cavities. In all these cases, owing to the short treatment distance, the geometry of source distribution is critical.
Figure a shows the images various techniques used in brachytherapy.
Brachytherapy may be used with people who have cancers of the head, neck, breast, uterus, cervix, prostate, gall bladder, esophagus, eye, and lung.Liquid forms of internal radiation are most often used with people who have thyroid cancer or non-hodgkin's lymphoma. You may also get internal radiation along with other types of treatment, including external beam radiation, chemotherapy, or surgery.
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5. The Physics of Radiation Therapy by F.M.Khan