Radiation Therapy
Radiation is a beam or field of intense energy focused on a certain area or organ of the body. It can be generated by a radioactive substance (such as cobalt) or with an atomic particle (linear) accelerator. In other strategies, a radioactive substance may be injected into a vein to travel to the cancer (for example, radioactive iodine, which is used in treatment of thyroid cancer, or radioactive implants, which may be placed directly into the cancer). A linear accelerator directs the radiation to the tumor, while normal tissue is shielded as much as possible. To reduce exposure of normal tissue to the beam, multiple beam paths are used.
Radiation preferentially kills cells that divide rapidly. Cancer cells divide more often than normal cells and therefore are more likely than most normal cells to be killed by radiation. Nonetheless, cancer cells differ in how easily they are killed by radiation; some are very resistant and thus cannot be effectively treated with radiation therapy. Unfortunately, radiation can damage normal tissues adjacent to the tumor, especially tissues in which cells normally divide rapidly, such as skin, the bone marrow, hair follicles, and the lining of the mouth, esophagus, and intestines. Radiation can also damage the ovaries or testes. A doctor tries to accurately target the radiation therapy to protect normal cells.
Radiation therapy is divided into a series of doses over a prolonged period of time. This method increases the lethal effects of the radiation on tumor cells, while decreasing the toxic effects of the radiation on normal cells. The latter effect occurs because normal cells have the capacity to repair themselves quickly after being exposed to radiation.
Radiation therapy plays a key role in curing many cancers, including Hodgkin's disease, early-stage non-Hodgkin's lymphoma, squamous cell cancer of the head and neck, seminoma (a testicular cancer), prostate cancer, early-stage breast cancer, early-stage nonsmall cell lung cancer, and medulloblastoma (a brain or spinal cord tumor). For early-stage cancers of the larynx and prostate, the rate of cure is essentially the same with radiation therapy as with surgery.
Radiation therapy can reduce symptoms when a cure is not possible, as in multiple myeloma and advanced lung, esophageal, head and neck, and stomach cancers. By temporarily shrinking the tumors, radiation therapy can be given as palliative therapy to relieve symptoms caused by spread of cancer to bone or brain.
New techniques of intense and highly focused radiation therapy, such as proton radiation, can effectively treat certain tumors in areas where damage to normal tissue is a worry, such as the eye, brain, or spinal cord. Radioactive seed implants (small pellets of a radioactive substance) are often used to treat prostate cancer. These seed implants provide intense radiation to the cancer and little to surrounding tissues.
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