Modelling Radiation Transport in Voxel Geometries with the Monte Carlo Code Mcnpx

Numerical methods for the simulation of radiation transport, in particular Monte Carlo techniques, are playing a fundamental role in the field of dosimetry for radiation protection. For the last 30 years or so, reference quantities have been since about 30 years calculated relying on mathematical analytical human phantoms representative of the standard man. These calculations, in large part based on Monte Carlo techniques, allowed large sets of conversion coefficients between physical quantities (such as radiation fluence) and dose related quantities (such as organ equivalent dose or effective dose) to be produced and transfer coefficients to be used for internal dosimetry purposes. For some years more detailed mathematical human phantoms based on Computer Tomography or Magnetic Resonance (voxel phantoms) have been implemented and are nowadays increasingly used both in the medical physics field and in the radiation protection fields thanks to the large computer power currently available. The present paper summarizes the research activities carried out at ENEA Bologna to develop a voxel option within the Monte Carlo code MCNPX. Examples of application in the field of external and internal dosimetry are given.