Radiation Therapy involves the use of x-rays, electrons, and radioactive sources in the treatment of cancer. This radiation is similar to x-rays used in the diagnosis of disease except that a much larger radiation dose and energy is used in a targeted fashion for cancer treatments. Like diagnostic x-rays, the radiation used in cancer treatments cannot be seen or felt. The doses of radiation used in treatment do not kill all cancer cells outright. Instead, radiation damages the cell's ability to reproduce itself. Cancer cells grow in rapid, uncontrollable fashion and are injured more readily than normal cells. Because of this, radiation must often be given over a period of a few weeks.
Radiation treatment may be delivered from a treatment machine outside the body directed at the cancer site. This is called External Beam radiation therapy.
In some cases, radiation may be applied internally. This form of radiation therapy is called Brachytherapy. The radiation is applied as close as possible to the tumour site, through insertion of radioactive seeds through tissue or radioactive sources through applicators into a body cavity.