Total body irradiation before bone marrow transplantation - Technique and acute toxicity

Purpose: To evaluate the total body irradiation methods in the National Ins titute of Oncology between January 1984 and February 1998. Patients and Methods: One hundred and twenty-four patients underwent total body irradiation prior to bone marrow transplantation in the last 15 years. A special cobalt unit has been used, the dose rate was 6 to 8 cGy/min in t he midline of the abdomen. The source-midline distance (SMD) was 340 cm and the field size was 80 x 200 cm. The dose calculation was done on the basis of a tissue-phantom ratio curve measured in total body irradiation conditi ons and effective tissue thickness (ETT). Between 1984 and 1992 the beam di rection was horizontal, the patients laid in lateral position. In II cases the total dose to the abdominal midline was 10 Gy, in 1 fraction. From 1986 the fractionation changed to 4 x 3 Gy. in 4 days. With individual lung shi elding the average lung dose was 8.5 Gy. In 43/124 cases the order of condi tioning treatment was chemo-radiotherapy. Since 1992 vertical beams were us ed, and the patients (80/124) laid in prone/ supine position. The fractiona tion remained the same but radio-chemotherapy regime has been used. Results: The irradiation in prone position proved to be safer than lateral because of smaller patient motion and it resulted in a more accurate positi oning of lung shielding, too. In all cases, the acute side effects (headach e, nausea, vomiting) were moderate. Using radio-chemotherapy the acute side effects during the total body irradiation were uncommon and well tolerable . Conclusion: Our technique with the large source-midline distance, vertical beam direction and the supine/prone position is stable, convenient and safe to produce homogeneous dose distribution and ensures accurate and reproduc ible lung shielding.