Determination of the dose rate constant through Monte Carlo simulations with voxel phantoms.

Purpose: The main goal of this study was to determine the dose rate constant of radionuclides used in Nuclear Medicine when they are biodistributed in humans. The secondary goal was to calculate the effective half-life for the same radionuclides in order to determine the realistic dose due to the incorporation of these nuclides for a variety of reasons.

Methods: Anthropomorphic voxel phantoms, with characteristics based on ICRP-110 were considered and the biodistributions of radionuclides were simulated using the Monte Carlo code MCNPX. In addition, the effective half-lives for all simulated radionuclides were calculated.

Results: The results for the dose rate constant, taking into account the patient body attenuation, showed no correlation between the biodistribution of the radionuclide and the energy of the radiation emitted. Body attenuation ranged between 6.7% and 94.1%. Also, the priority angle of radiation emission was determined. The values found for the body attenuation agree with the literature, corroborating the calculation of the body dose rate constant.

Conclusions: The results for the body dose rate constant calculated in this work, for 30 radionuclides and 57 radiopharmaceuticals, and their effective half-lives, may be used to estimate the dose emitted by a person who has incorporated a radionuclide in the Nuclear Medicine activity range. This dose will be optimized when the body dose rate constant and the effective half-life determined in this study are used together with dose reduction factors.