Radiation therapy uses high-energy radiation to shrink tumors and kill cancer cells. X-rays, gamma rays, and charged particles are types of radiation used for cancer treatment. The radiation may be delivered by a machine outside the body called a linear accelerator to focus x-rays directly on the tumor or tumor bed (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy, also called brachytherapy). Systemic radiation therapy uses radioactive substances, such as radioactive iodine, that travel in the blood to kill cancer cells.
Doctors may use radiation therapy to relieve pain caused by the tumor, to try to shrink the tumor before surgery or to destroy cancer cells that may remain in the area after surgery. About half of all cancer patients receive some type of radiation therapy sometime during the course of their treatment. Radiation therapy kills cancer cells by damaging their DNA (the molecules inside cells that carry genetic information and pass it from one generation to the next). Radiation therapy can either damage DNA directly or create charged particles (free radicals) within the cells that can in turn damage the DNA.
Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and eliminated by the body’s natural processes. Radiation therapy can also damage normal cells, leading to side effects. Doctors take potential damage to normal cells into account when planning a course of radiation therapy. The amount of radiation that normal tissue can safely receive is known for all parts of the body. Doctors use this information to help them decide where to aim radiation during treatment. Key Points * Radiation therapy uses high-energy radiation to kill cancer cells by damaging their DNA.
* Radiation therapy can damage normal cells as well as cancer cells. Therefore, treatment must be carefully planned to minimize side effects. * The radiation used for cancer treatment may come from a machine outside the body, or it may come from radioactive material placed in the body near tumor cells or injected into the bloodstream. * A patient may receive radiation therapy before, during, or after surgery, depending on the type of cancer being treated. * Some patients receive radiation therapy alone, and some receive radiation therapy in combination with chemotherapy.