Radiation Oncology - also called radiation therapy or radiotherapy - uses ionizing radiation in its various forms to treat human disease. Although radiation is most often used to treat malignant disease or cancer, it plays an important role in several non-cancerous conditions. The most commonly used radiation source is a linear accelerator which produces high energy x-rays. This very sophisticated machine also focuses and shapes the x-ray beam so as to treat the desired target while minimizing radiation dose to the transited and surrounding tissue and normal body structures.
Ionizing radiation is used not only to treat cancer, but also in reducing or palliating symptoms of cancer when it is no longer treatable but has spread to other organs.
The precise mechanism by which radiation kills cancer cells is unclear. When administered in a single large dose fraction, it probably kills by direct disruption of the reproductive system in cancer cells. On the other hand, when administered in a fractionated manner over several weeks, it works primarily by destroying the newly formed and possibly defective endothelial or blood vessel cells that the cancer cells force the body to form in order to maintain their existence and growth. Some types of cancer are very sensitive to low doses of radiation and are killed by direct interaction with radiation and DNA.