Monte Carlo Estimation of Patient Effective Dose in Diagnostics Procedures Using I-131

Therapeutic or diagnostic radiopharmaceutical capsule containing (NaI)-I-131 stays in stomach for 15 minutes before the absorption starts, long enough to make possible risky exposure. During the oral application it is reasonable to measure effective dose in stomach. Direct measurements of organ doses are not possible so there is a strong recommendation to estimate them by calculation. The main goal is the I-131 risk assessment. Monte Carlo code MCNP4b was used to model the transport of gamma and beta particles emitted by radionuclide I-131 considered as a point source at the bottom of the stomach. Absorbed energy per unit transformation in stomach and surrounding organs has been calculated. The dose equivalents in these organs have been calculated in aim to determine the effective doses using appropriate tissue weighting factor values. Obtained results had not significant importance for radiation protection but they were important for establishment of new calibration procedures as a part of QA and QC programs in radiopharmaceuticals production and control.