Oncology Radiation Systems is branch of radiology that deals with the use of ionizing radiation to treat cancers. The radiation therapy tumors are made up of cells that are reproducing at abnormally high rates. Radiation therapy specifically acts against cells that are reproducing rapidly. Normal cells are programmed to stop reproducing (or dividing) when they come into contact with other cells. In the case of a tumor, this stop mechanism is missing, causing cells to continue to divide over and over. It is the DNA of the cell that makes it capable of reproducing. Radiation therapy uses high energy x-rays to damage the DNA of cells, thereby killing the cancer cells, or at least stopping them from reproducing. Radiation also damages normal cells, but because normal cells are growing more slowly, they are better able to repair this radiation damage than are cancer cells. In order to give normal cells time to heal and to reduce a patient's side effects, radiation treatments are typically given in small daily doses, five days a week, over a six-or seven-week period. It is estimated that more than 50% of cancer patients will receive radiation at some point during their treatment.