Dose calculation with MCNPX code for Total Body Irradiation technique in sitting and lying postures

Total Body Irradiation (TBI) is a radiotherapy technique used to destroy malignant cells in bone marrow transplant conditioning regimens. The aim of this work was to estimate the equivalent and effective doses in TBI computational scenarios to analyze the changes in these quantities for different sources (cobalt-60 source and 6 MV photon beam), postures of the phantom, irradiation geometries, backscatter factors, and attenuators. The simulations were performed in MCNPX code using hybrid phantoms from the University of Florida. The simulation results showed uniform equivalent doses for the phantoms in the lying posture. It is also observed that when the phantoms are closer to a wall, there is an additional dose contribution of up to 6.55% to organs near to this structure. When the lead attenuators for the lungs are not present in exposure scenarios, the equivalent dose increases by more than 20%. For the effective dose, the values are considerably higher for the left lateral projection due to the greater energy absorption by more radiosensitive organs. The results of the simulations reaffirm the data found in the literature about TBI procedures.