Treatment of cancer and, occasionally, some noncancerous tumours, by X-rays or other radiation. Radioactive sources produce ionizing radiation, which destroys or slows down the development of abnormal cells. Normal cells suffer little or no longterm damage, but short-term damage is a side effect. Radiotherapy may be used on its own in an attempt to destroy all the abnormal cells in various types of cancer, such as squamous cell carcinoma and Hodgkin’s disease. It may also be used with other cancer treatments. Surgical excision of a cancerous tumour is often followed by radiotherapy to destroy any remaining tumour cells. Radiotherapy may also be used to relieve the symptoms of a cancer that is too advanced to be cured. If benefits outweigh risks, radiotherapy may be used to treat noncancerous diseases; for example, part of an overactive thyroid gland (see thyrotoxicosis) may be destroyed using radioactive iodine. Radiotherapy is usually performed on an outpatient basis. X-rays (or sometimes electrons) produced by a machine called a linear accelerator are aimed at the tumour from many directions. This produces a large enough dose of radiation to destroy the tumour. Alternatively, a source of radiation, in the form of tiny pellets, is inserted into the tumour through a hollow needle (see interstitial radiotherapy) or into a body cavity (see intracavitary therapy). Radioactive iodine used to treat thyrotoxicosis is given in liquid form and drunk through a straw. There may be unpleasant side effects, including fatigue, nausea and vomiting, and loss of hair from irradiated areas. Rarely, there may be reddening and blistering of the skin.


Online Medical Dictionary: Your essential reference to over 5000 medical terms.