Radiation therapy is the use of high energy x-rays or other particles to kill cancer cells. If you need radiation therapy, you will be asked to see a specialist called a radiation oncologist, a doctor who specializes in giving radiation therapy to treat cancer. The most common type of radiation treatment is called external-beam radiation therapy, which is radiation given from a machine outside the body. When radiation treatment is given using implants, it is called internal radiation therapy or Brachy Therapy. A radiation therapy regimen (schedule) usually consists of a specific number of treatments given over a set period of time.