Physical problems of total body irradiation.

In the concept of combined treatment of acute leukemias the whole body has to be irradiated as precisely and homogeneously as reasonably achieveable. In fulfillment of these radiobiological requirements, total body irradiation (TBI) means a very special challenge to medical physicists. Very large, uniform high energy photon beams have to be realized and applied. The dose at any relevant reference point has to be determined, regarding all influences of the TBI treatment situation. The dose distribution has to be modified - if necessary - verified and recorded. The lungs - the vital organs at risk in TBI - have to be shielded to tolerable doses. Optimization of TBI demands to understand all physical limitations and to utilize all technical possibilities. These physical problems encountered with TBI dosimetry, treatment planning and treatment performance are discussed.