Radiation therapy, also called irradiation or radiotherapy, is the use of high-energy x-rays to kill cancer cells. A large machine called a linear accelerator directs x-rays to the precise portion of the body needing treatment. The radiation is given in doses measured in units called centigray (cGy) or gray (Gy).

Radiation is usually given every day for a specific number of days, excluding weekends. This process is called standard or conventional fractionation, and it is the most common way radiation is given to children and teens with leukemia. Radiation given more than once a day is called accelerated fractionation, or hyperfractionation. It uses smaller amounts of radiation for each treatment.