Physical aspects of total body irradiation of bone marrow transplant patients using 18 MV x rays

The physical aspects of a total body irradiation (TBI) treatment are described. Patients seated in a special chair with their legs bent backwards are irradiated anteriorly and posteriorly (AP/PA). The chair reduces patient movement and facilitates positioning patients during 9 fractions of TBI over a 3-day period. The dose to lower extremities are monitored and raised to the total body dose. A conventional linear accelerator in a standard size treatment room is used to deliver 18 MV x-ray beams at a dose rate of approximately 20 cGy/min at a 350 cm treatment distance. Results of dose distribution, field flatness, dose uniformity, in vivo and in vitro dosimetry, and boost irradiation techniques are described.