A type of radiation therapy that is given to the entire body. Total-body irradiation is often used with high-dose anticancer drugs to help prepare a patient for a stem cell transplant. It is done to kill any cancer cells that are left in the body and helps make room in the patient’s bone marrow for new blood stem cells to grow. Total-body irradiation may also help prevent the body’s immune system from rejecting the transplanted stem cells. Also called TBI.