RADIATION THERAPY

also called Radiotherapy, or Therapeutic Radiology, use of radiation sources in the treatment or relief of diseases. Radiation therapy almost always makes use of ionizing radiation, deep tissue-penetrating rays, which can physically and chemically react with diseased cells to destroy them. The other forms of radiation, infrared and ultraviolet, can be employed in heat lamps for neuritis and arthritis conditions to relieve the inflammation. Radiation therapy is used for cancer and for blood disorders such as leukemia. Formerly it was used for overactive thyroids, acne, and benign tumours, but complications with more severe skin diseases and radiation-induced cancers caused almost complete abandonment of these procedures. Radiation may be administered to the body by implanting radioactive substances into the tumours or by exposing the body to external sources of high-energy rays that penetrate internally. Both methods have met with fairly good results in the cure or arrest of cancerous growths; the type of treatment used depends largely on the size of the tumour, its location, the degree of radiation desired, and the most convenient method for the individual's circumstances. The purpose of such radiation therapy is to destroy cancerous cells with minimal damage to normal healthy tissue or systemic involvement. Ionizing radiation bombards the cells exposed to it and breaks the molecular bonds essential to cell growth. There is always the accompanying destruction of some normal tissue along with the tumour. Cancer growths that reproduce rapidly are generally more easily eradicated by radiation than slower-growing ones; some tumours are destroyed by irradiation treatment, while others are unaffected by it. The complications of radiation therapy may include vomiting, nausea, hair loss, weight loss, weakness, drop in blood levels, and skin disorders. Easily accessible tumours of fairly small size are often treated by implantation of radioactive wires, threads, seeds, tubes, molds, or foams. The radiation sources can be radium and radon, or radioactive isotopesradioactive forms of such metals as cesium, cobalt, gold, iridium, and tantalum. All of these isotopes emit gamma rays, which produce deep penetration and cause a minimum of surface-tissue irradiation. The elements are sealed in glass tubes, wires, or needles for easy tissue insertion and an even distribution of radiation. The implants can be permanent or temporary. The radiation dose by this method is usually slow and continuous, which gives the more resilient normal cells time to repair any damage that might be inflicted on them while the cancer cells are being destroyed. The advantages of implantation are that the tumour can be treated locally without involving other areas of the body; the radiation is continuous; the rays can be directed to conform to specific structural contours, as in the bladder, uterus, or mouth; and there is minimum deformity and interference with function. Tumours respond best to this therapy if they are small, rapidly growing, and discovered early. External radiation must penetrate the outer body and reach the tumour. More normal tissue is affected this way, but larger growths are more readily cured. The treatments involve a series of about 10 to 20 radiation sessions over a period of several months. This type of therapy is frequently used in conjunction with surgical removal of the growth; it may serve, however, as the sole means of treatment when surgery is impossible. Its advantage over implantation is that higher doses can be administered to deep-seated tumours.