  Monte Carlo (MC) techniques are currently deemed the gold standard for
internal dosimetry, since the simulations can perform full radiation transport
and reach a precision level not attainable by analytical methods. In this
study, a custom voxelized particle source was developed for the TOPAS-MC
toolkit to be used for internal dosimetry purposes. The source was designed to
allow the use of clinical functional scans data to simulate events that
reproduce the patient-specific tracer biodistribution. Simulation results are
very promising, showing that this can be a first step towards the extension of
TOPAS-MC to nuclear medicine applications. In the future more studies are
needed to further ascertain the applicability and accuracy of the developed
routines.
