Radiation therapy is a form of cancer treatment that uses an intense form of energy, called ionizing radiation, to damage or destroy cancer cells. Ionizing radiation harms cancer cells' genetic material. This kills the cells or interferes with their ability to grow and multiply. Normal cells near a tumor can be damaged as well. However, normal cells can repair any damaged genetic material, so they often recover and survive. Cancer cells generally can't make such repairs, so they die.
Radiation therapy can be given externally in the form of x-ray beams, gamma rays, or beams of subatomic particles such as protons. Treatment with external radiation is usually painless and takes five to 15 minutes per session. The number of treatments varies for each person. In some cases, therapy may take place almost every day for several weeks.
Radiation also can be delivered internally. Radioactive substances are either placed inside a body cavity or implanted inside the tumor itself.
Some doctors use these techniques to increase the effectiveness of radiation therapy:
Conformal beam techniques — Radiation is delivered from many beams at the same time. This allows the radiation to be concentrated on the tumor with less damage to nearby normal tissues.
Intraoperative radiation therapy — Radiation is delivered to a tumor during surgery.
Radiosensitizers — These drugs increase radiation's damaging effect on cancer cells.
Radioprotectors — These drugs protect normal cells from radiation damage while nearby cancer cells are destroyed.
Radioimmunotherapy — Radioactive substances are attached to antibodies, defensive chemicals made by the body's immune system. These antibodies target cancer cells and deliver damaging radioactivity only to them. Because the antibodies do not attack healthy cells, the possibility of radiation damage outside the tumor drops.