Radiation therapy, the use of X rays and other forms of radiation to treat cancer, is truly a twentieth-century medical specialty. About half of the more than 900,000 patients who are diagnosed as having cancer each year in the United States will undergo radiation therapy. Very often the radiation treatments will be combined with surgery and chemotherapy.
But more than 100,000 cancer patients are rendered free of the disease each year by radiation therapy alone. These advances are due to a number of factors, including the use of different kinds of radiation in cancer treatment, a greater understanding of how cancers grow and react to radiation therapy, and the development of more precise diagnostic tools and computer-designed treatment plans to meet the needs of individual patients.
History Of Radiation Therapy
Radiation therapy can be traced to the discovery of uranium by the, French physicist Henri Becquerel in 1896 and to Marie and Pierre Curie, who identified the even more radioactive substances polonium and radium in 1898. For these discoveries, the three shared the Nobel Prize in physics in 1903. Parallel to these discoveries was the pioneering use of diagnostic X rays by the German researcher Wilhelm Conrad Roentgen, who discovered that these rays could be used to visualize the bones and other internal structures. Experiments using the new phenomenon to treat skin cancers followed soon after, with some striking successes.
It was also discovered that X rays could be used to treat some cancers of the cervix. But the early X-ray machines were relatively weak and could not penetrate into the body to reach deep tumors. Instead these conventional “orthovoltage” machines, with a range of 250 to 400 kilovolts (a kilovolt is one thousand volts), deposited much of their radiation close to the skin surface. This often caused burns and other skin problems, including later cancers (as was discovered years after the use of X rays to treat such conditions as acne and tonsillitis). But a series of rapid technologic advances have completely changed the nature of modern radiation therapy. By the 1950s radioactive cobalt, an artificial radioisotope that delivers higher energy rays with deeper penetration into the body and fewer skin problems than orthovoltage X-ray machines, came into use to treat a variety of cancers.
A decade later, in the 1960s, higher-energy supervoltage machines appeared. These could deliver rays of 4 to 40 megavolts (a megavolt is one million volts) with even deeper penetration but with still less skin damage. Today most radiation therapy units are equipped with several types of machines: a high-voltage beam, a cobalt machine, and a low-energy machine for skin cancers. A computerized system, often monitored by a major cancer treatment center, usually is employed to control the course of treatment. There are also instances in which radioactive materials are implanted directly into the tumor or close to it. The purpose is the same—namely, to employ radiation to destroy the fast-growing cancer cells with a minimum of damage to healthy tissue.