Development of a translating bed for total body irradiation

Total body irradiation is used to prepare a patient for bone marrow transplantation. Traditional techniques often sacrifice dose uniformity for patient comfort and ease of treatment. A method has been developed using a translational bed under a Cobalt 60 photon beam. The bed and controller were designed and built on site. A bolused patient lying in the bed is moved at constant speed through the beam. Using this technique, dose homogeneity is optimized by the use of bolus, extended source-skin distance, adequate field size and use of anterior/posterior fields. The dose rate represents a compromise between a value high enough to keep treatment times tolerable by the patient and one that is sufficiently low to avoid treatment complications. The value of 50 cGy/min which was used meets these requirements. Extensive phantom measurements have shown that the dose homogeneity can be obtained to within an acceptable limit of +/- 5%.