A fractionated X-ray total body irradiation technique with patients lying on side and in vivo dosimetry analysis

Objective: To investigate an X-ray total body irradiation (TBI) technique using anterior-posterior opposed fields with patients at the side-lying position, and to analyze the real-time in vivo dosimetry results. Methods: The accelerator with 10 MV X-rays of Varian Trilogy was used for the TBI with the extended source to skin distance of 390 cm. The percent depth dose, off axis factors and absolute dose output were measured. The dose accuracy and homogeneity was monitored real-time using multi-channel diode dosimeter for 10 patients. The monitored sites included forehead, mandible, suprasternal fossae, xiphoid, umbilicus, pelvis, middle of thigh, knee, middle of leg and ankle. The patients were irradiated at the side-lying position, with the prescription dose of 1200 cGy/6 f during 3 days, the middle line dose rate of 5.0 cGy/min. Solid water was used for the compensation of the dose homogeneity. Results: The off axis dose homogeneity was less than ± 5.0% for the TBI geometry. The absolute dose output was 0.0721 cGy/MU at the maximum dose point. The total body irradiation was finished smoothly for the 10 patients lying on side. The deviation of monitored total dose from the total prescription dose was within -4.9% to 6.7% for the 10 monitored sites. The monitored dose homogeneity was less than 5.0%. Conclusions: The fractionated anterior-posterior opposed parallel TBI can be finished smoothly with patients side-lying. Accurate and homogenous dose distribution can be obtained using real-time dose monitoring and compensation with solid water. (authors)