In external beam radiation therapy, radiation is produced by a machine called a linear accelerator. Short bursts of x-rays are fired from the machine at your cancer. The x-rays come out in a square-shaped manner, and the radiation oncologist designs special blocks or uses special columnators within the machine itself to shape the radiation beam so that it treats the cancer and as little normal tissue as possible.

In general, radiation is not used in the treatment of leukemia, except when a patient is being prepared for bone marrow transplant or in some cases of chronic leukemia. Sometimes local irradiation to the spleen may be needed if large numbers of leukemia cells are clogging that organ; in such a situation, irradiation may be an alternative to surgical removal of the spleen.