Monte Carlo methods in nuclear medicine

Monte Carlo (MC) simulation of the radiation transport and interaction in matter finds an ever-increasing application in nuclear medicine. Starting from a general summary of the principles of MC approach, an overview of the several general-purpose MC codes (GEANT4, MCNP, EGS, PENELOPE, FLUKA), dedicated codes (SIMIND and others) and interfaces specifically developed for medical radiation physics and nuclear medicine applications (GATE, GAMOS and others), are presented. The most relevant fields in which MC simulation has an established role in nuclear medicine are internal dosimetry, instrumentation design and optimization, radiation protection and radionuclide production. Internal dosimetry models, at organ or voxel level, have been successfully developed. MC simulations can be also employed for patient-specific 3D dosimetry based on SPECT-CT and PET-CT data. Concerning imaging devices, the optimization of all the parameters influencing the detector response and image quality, also for innovative scanner architectures, can be deeply investigated. On the other side, existing PET and SPECT tomographs can benefit of MC-derived correction factors. In radiation protection from radionuclides used in diagnostic and therapeutic procedures, MC approach reveals to be a powerful tool for estimating exposures, even in complex environmental conditions, for designing radiation shielding, particularly in the case of high-energy therapeutic beta emitters. Radionuclide production goes through several nuclear reaction processes, induced in most cases by proton or neutron beams. Target assembly, including the choice of target material and shape, and beam features, must be optimized to achieve an optimal production yield and radionuclide purity. Finally, MC simulation shows its potential in supporting the effective teaching of radiation-matter interaction concepts, applied in nuclear medicine.