Total body irradiation with megavoltage photon beam is most commonly used as part of the conditioning regime for bone marrow transplantation used in the treatment of a variety of diseases such as leukemia, aplastic anemia, lymphoma, multiple myeloma, autoimmune diseases, inborn errors of metabolism, and other illnesses. The role of TBI is to destroy the recipient’s bone marrow and tumor cells, and to immunosuppress the patient sufficiently to avoid rejection of the donor bone marrow transplant. In most cases, the patient will undergo a chemotherapy conditioning program before the TBI and bone marrow transplant. Although chemotherapy alone can be used as a conditioning regimen, addition of TBI is considered beneficial for certain diseases and clinical conditions.

TBI is delivered using a  linear accelerator through anterior and posterior fields in a standing upright position at the TBI distance. A special treatment room is available for large-field irradiation.

The principle of the technique is that standing TBI allows shielding of certain critical organs from photons and boosting of superficial tissues in the shadow of the blocks with electrons. For example, dose to the lung tissue can be reduced using lung blocks and the chest wall under the blocks can be boosted with electrons of appropriate energy.