radiotherapy(redirected from radiography episode)
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the therapeutic use of several kinds of ionizing radiation of varying energies.
Radioactivity was found to have a biological effect on the body shortly after the discovery of radioactive substances by A. Becquerel in 1896 and the study of them by P. Curie. (Originally, radiotherapy was called curietherapy.) The French physicians E. Benier and H. Denlaut were the first to use irradiation with radium for therapeutic purposes (1897). Further research revealed that young, rapidly growing and multiplying cells were the most sensitive to the process; this became the basis for using radioactive radiation to destroy malignant tumors, which consist of such cells.
There are many kinds of radiotherapy, including alpha, beta, gamma, neutron, pi-meson, proton, X-ray, and electron. The use of radiotherapy is based on a number of factors. First, ionizing radiation induces functional and anatomical changes in tissues, organs, and the body as a whole. It suppresses the capacity of cells for growth and multiplication and causes the death of tissue elements of the irradiated organ. (The extent of injury to the irradiated tissues is directly proportional to the dose absorbed.) Second, pathologically altered tissues (tumorous, degenerative, or inflamed) are more sensitive to radiation than are normal tissues. Finally, the use of radiotherapy is based on the response of the body and of the individual organs and tissues to irradiation.
Slight radiation injury is reversible, and the response of irradiated tissue is manifested in compensation for or even intensification of the diminished or lost function. With deep anatomical injuries to irradiated tissues, however, the process is irreversible, and the dead elements are replaced by nonfunctional connective tissue. Therefore, in some cases, the purpose of radiotherapy is either to intensify or to suppress the function of the given organ. In other cases (for example, with such malignant tumors as cancer or sarcoma) the intention is to suppress vital activity completely and destroy the pathologically altered tissues.
An important prerequisite for effective radiotherapy is the choice of radiant energy and the dose to be absorbed by the tissues. Radioisotopes (60Co, 137Cs, 32P, 198Au, 137I, 192Ir), X-ray equipment, gamma-ray sources, and charged-particle accelerators (linear accelerators, cyclotrons, and betatrons) are used as sources of ionizing radiation.
Depending on the location of the source of radiation in relation to the irradiated organ, irradiation is described as internal or external. Internal irradiation is produced by introducing a radioactive substance orally or intravenously; the substance, which emits charged particles and gamma rays, gradually distributes itself in the various organs and tissues. External irradiation may be general (whole-body) or local. Whole-body irradiation is used only rarely; the local irradiation of an organ or a limited part thereof (with the other parts shielded) is the principal method of radiotherapy.
Remote irradiation (teletherapy) is used to treat deep-lying foci. The radiation source (gamma sources, X-ray machines, accelerators) is placed at a considerable distance from the skin (30-120 cm). Short-focus irradiation, in which the source (X-ray machines or devices with a 60Co or 192Ir charge) is kept no more than 3-7 cm from the skin, is the method generally used to treat skin diseases, especially malignant tumors. Skin diseases are also treated by contact irradiation or by the application to the skin or mucous membrane of radioactive preparations emitting alpha or beta particles.
Various methods are used for intracavitary irradiation. The small tube of a special close-focus X-ray machine is inserted directly into a body cavity, such as the mouth, vagina, or rectum. A rubber balloon filled with a solution of the radioactive substance, a metal case with tubes containing a radioisotope, or beads of 60Co are inserted into cavitary or tubular organs, such as the urinary bladder, uterus, or bronchus. A solution or suspension of a radioactive isotope can be injected into an organ or into the pleural or abdominal body cavity.
Interstitial irradiation is achieved by introducing needles or tubes containing 60Co or 192Ir into the tissues. Colloidal solutions containing 198Au or granules of 198Au can also be introduced into the tissues. Radiotherapy is commonly combined with surgery, drug therapy, hormonal preparations, dietary regulation, and other types of treatment, since a combination of methods is most effective.
REFERENCESDomshlak, M. P. Ocherki klinicheskoi radiologii. Moscow, 1960.
Kozlova, A. V. Metodika primeneniia radioaktivnykh izotopov s lechebnoi tsel’iu. Moscow, 1960.
Kozlova, A. V. Luchevaia terapiia zlokachestvennykh opukholei. Moscow, 1971.
Luchevaia terapiia s pomoshch’iu izluchennii vysokoi energii. Moscow, 1964. (Translated from German.)
Fizicheskie osnovy luchevoi terapii i radiobiologii. Moscow, 1969. (Translated from French.)
Spravochnik po rentgenologii i radiologii. Edited by G. A. Zedgenidze. Moscow, 1972.
G. A. ZEDGENIDZE