CAN A TOTAL-BODY IRRADIATION TECHNIQUE BE FAST AND REPRODUCIBLE

Purpose: Total body irradiation (TBI) is frequently a complex and time -consuming technique that significantly overloads Radiation Oncology d epartments. In an attempt to shorten TBI setup and treatment time we a imed to develop a system where the lung blocks are fixed with optimal precision to the build-up booster lucite screen while the patient is i mmobilized in a reproducible upright position. Methods and Materials: Fifteen patients diagnosed with leukemia were conditioned before bone marrow transplant since March 1992. Patients were immobilized in a sem istanding position in a special stand with arm bars and hand grips. Tr eatment was delivered with a 6 MV x-ray horizontal beam. Six fractions of 2.25 Gy (mean instantaneous dose rate of 13.8 +/- 3.8 cGy/min) wer e delivered twice a day over 3 days (total dose: 13.5 Gy). Each fracti on was given in alternating AP (facing the beam) and PA (turning the b ack) projections. Customized lung blocks (35% transmission) were used to assure a maximum lung dose of 10 +/- 0.5 Gy. The blocks were taped to a 1 cm thick lucite screen interposed between the source and the pa tient. Lung shields were checked by port films before each fraction. T he reproducibility of the patient's positioning (and lung shielding) w as evaluated by measuring the horizontal and vertical deviations of th e infero-external corners of the lung blocks in the port films in rela tion to the same point in the simulation films. In vivo dosimetry (the rmoluminiscence and diodes) was performed by placing dosimeters and pr obes in the central axis and in several off-axis sites. Results: The m ean horizontal and vertical deviations were 3.5 +/- 4.1 mm and 7.5 +/- 5.9 mm for the anterior fields, and 4.1 +/- 4.1 mm and 6.9 +/- 6.4 mm for the posterior fields. An acceptable position of the blocks was co nsidered when deviations were < 5 mm horizontally and/or < 10 mm verti cally. The mean time per fraction (i.e., interval between the patient' s entering and leaving the treatment room) was 35 +/- 5 min. Conclusio ns: A satisfactory level of reproducibility can be reached with this t echnique. The reasonably short treatment time contributes to reproduci bility and patient comfort.