James C. H. Chu, PhD
Rush University Medical Center
Chicago, IL 60612
Total body irradiation is often used to eradicate diseased bone marrow and leukemic cells and/or to provide immunosuppression for patients receiving bone marrow transplant. The treatment can be delivered with a variety of techniques using megavoltage photon beams. The need to achieve a uniform dose distribution over a very large treatment volume while maintaining low doses to the critical organs presents a difficult challenge to a medical physicist. In addition, a physicist should be prepared to deal with many other technical issues. For example, the radiation beams are usually projected over a large distance to encompass the entire patient during TBI. However, this treatment geometry may not be possible for facilities with only small treatment rooms. Other medical physics issues related to TBI include, among others, the need of a large phantom for beam data acquisition, the validity of inverse square fall off over a large distance, the effect of scatter when the patient is positioned close to the wall, the dose to marrow when the bone is relatively superficial, the establishment of a dose prescription system, the use of in vivo dosimetry, the use of beam spoiler and bolus, and the shielding of lungs and kidneys.