RESUMEN
PURPOSE: Total body irradiation (TBI) is frequently a complex and time-consuming technique that significantly overloads Radiation Oncology departments. In an attempt to shorten TBI setup and treatment time we aimed to develop a system where the lung blocks are fixed with optimal precision to the build-up booster lucite screen while the patient is immobilized 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 semistanding position in a special stand with arm bars and hand grips. Treatment 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) were delivered twice a day over 3 days (total dose: 13.5 Gy). Each fraction was given in alternating AP (facing the beam) and PA (turning the back) 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 patient. Lung shields were checked by port films before each fraction. The reproducibility of the patient's positioning (and lung shielding) was evaluated by measuring the horizontal and vertical deviations of the infero-external corners of the lung blocks in the port films in relation to the same point in the simulation films. In vivo dosimetry (thermoluminescence and diodes) was performed by placing dosimeters and probes in the central axis and in several off-axis sites. RESULTS: The mean 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 considered when deviations were < 5 mm horizontally and/or < 10 mm vertically. The mean time per fraction (i.e., interval between the patient's entering and leaving the treatment room) was 35 +/- 5 min. CONCLUSIONS: A satisfactory level of reproducibility can be reached with this technique. The reasonably short treatment time contributes to reproducibility and patient comfort.
