Radiation.
Use of radiation to treat cancer dates from the late nineteenth century, following soon after the discovery of X rays in 1895 and of natural radiation in 1896. Radiation consists of high-energy waves or particles produced by electromagnetic devices (e.g., high-voltage vacuum tubes) or radioactive elements and their compounds. Very high-energy radiation has the capacity to produce ionization, knocking electrons out of their atomic orbits in matter that it strikes. Ionizing radiation includes waves, such as X rays and gamma rays, and particles, such as neutrons and protons. Only ionizing radiation is used in cancer therapy and, as late as the 1980s, only waves. In the late twentieth century, devices using conventional X-ray tubes and cobalt-60 sources of radiation were largely replaced by much higher-energy equipment, such as linear accelerators. Higher-energy sources produce more penetrating, sharply focused radiation beams, delivering more destructive power to diseased areas while sparing healthy tissue from exposure.
When absorbed by living tissue, radiation causes death or damage to the cells. Much of a cell is composed of water, from which radiation produces a variety of compounds and ionized particles. While short-lived, these particles rapidly combine with cell proteins, interfering with their normal function in the cell. Ionizing radiation produces compounds that break apart DNA, vital for cell reproduction. Radiation destroys cancer tissue by killing individual cells or limiting their ability to reproduce. Tumors do not seem to be able to maintain themselves if a significant proportion of their cells lose the ability to replicate.
Doctors have several options for delivering radiation to a tumor. Those most often used are external beams generated by electromagnetic devices or implants containing radioactive substances placed inside the body. External beam therapy can deliver radiation through the skin and other tissues, concentrating greatest energy on the specific internal location
targeted for therapy. Focusing beams from several angles results in concentration at the desired spot while sparing healthy tissue.
Interstitial radiation therapy involves implantation of a radioactive source within the body in close proximity to the diseased tissue. In treating prostate cancer, for example, physicians may implant radioactive gold or iodine in the form of seeds or needlelike stilettes in the tissue bed from which a tumor has been removed. These implants deliver radioactivity to the exact area desired and continue doing so for months without interruption.[5]
H. J. G. Bloom, "Radiotherapy," Recent Results in Cancer Research 78 (1981): 132-53.
Physicians may implant grains of radioactive material near tumors in deep-lying organs such as the liver, threading catheters bearing these materials through large veins to reach their targets.While radiation may play the primary role in treatment of some cancers, it is often used as a follow-up procedure for surgery. Physicians may perform radiation therapy to treat malignant tissue that surgeons are not able to remove. In addition, radiation may be used as "adjuvant" therapy; that is, treatment for disease that is not apparent but is suspected of existing or thought likely to develop at a later time. Patients receiving surgery for mouth cancers, for example, may later receive radiation therapy to nearby lymph nodes, even though they show no signs of metastases. Patients with small cell lung cancer may receive prophylactic radiation to the skull. The brain is a frequent target of metastases in this form of cancer, and resulting brain dysfunctions often prove the immediate cause of death.
Radiation therapy does not have the same heroic panache as surgery. External beam therapy is almost always performed on an outpatient basis; the patient receives this therapy in a specially designed room, awake, and often standing up. He or she usually sees, hears, and smells nothing extraordinary during the procedure, which is conducted as a series of treatments repeated over several weeks. Radioactive implants may be placed after the removal of a tumor in surgery but may also be deposited in nonsurgical procedures.
While less apparently intrusive than surgery, radiation has a powerful impact on the body. As in surgery, medical judgment is required to determine when and what kind of radiation may be beneficial. Radiation causes a variety of side effects, including loss of appetite, nausea, and damage to the linings of the esophagus and intestines. The mechanisms by which radiation therapy damages cells, moreover, can themselves give rise to cancer; patients undergoing radiation therapy have been known to develop additional tumors as a result of their treatment. Physicians
can reduce the immediate side effects of radiation therapy by scheduling intervals for recovery between radiation dosages.