Modeling, validation and case study of a whole body counter for in vivo measurements based on a CAD model imported into MCNP6.

This work presents the modeling and validation performed on a whole-body counter (WBC) system used for in vivo monitoring, aiming to obtain a model to be used in simulations of changes in the geometry and materials employed in the shielding, in order to enable improvements in the internal dosimetry measurements carried out with this system. After the validation of this model was completed, an initial case study was conducted to evaluate changes in the detector positioning. Computational simulations were performed using MCNP6 (Monte Carlo N-Particle Transport Code), employing the WBC geometry generated using CAD (Computer Aided Design) software, converted and imported into MCNP6 through the Visual Editor. In parallel, photon spectra from the monitoring room background were collected to be used as input for the source for simulation. The model was validated through comparison with experimental data from previous studies on detector shielding, in which the simulated results differed from the experimental data by less than 10%. This variation was considered acceptable for the validation of the model proposed in this study. In the case study, the change in detector positioning resulted in improved background shielding; however, there was a significant loss in detection efficiency. Since the contribution of these two variables in the evaluation of the minimum detectable activity is nonlinear, further assessments should be conducted to determine the effectiveness of this change in detector positioning.