Dosimetry of positrons from PET radiotracers using Monte Carlo simulations and measurements

Abstract

Positrons, the anti-particle of electrons, are broadly used in medicine and materials science. Thus, understanding how free positrons interact with soft biological matter is important for medical diagnostic procedures as well as for safety. Most research in this regard focuses on positron transport in the context of image quality; however, scholars lack knowledge regarding radiation dose exposure. Too little attention has been paid to the full analysis of positron internal dosimetry.In this paper we examine the quality of positron transport using EGS5 Monte Carlo (MC) code, comparing it to GAMOS Monte Carlo code. To validate the suitability of EGS5 and GAMOS codes for positron dose evaluations, an experiment with a concentrate FDG syringe was performed. Dose rate was measured using a mobile MOSFET device and compared to MC simulation results obtained by EGS5 and GAMOS. In this study simulations of the transport of mono-energetic positron beams from 100 keV to 1.2 MeV were performed, in addition to two practical radionuclide isotopes through two different tissue layers: 5 mm and 0.07 mm thickness. The results of the simulations using ESG5 Monte Carlo code were compared to the GAMOS Monte Carlo code results. The simulations were performed to obtain detailed energy deposition from interactions of positrons and secondary electrons induced by positron sources along tissue layers.The EGS5 code dose results demonstrate good agreement with the MOSFET measured results. The GAMOS code results yielded a difference of more than twice the measured dose. Differences between the EGS5 and the GAMOS codes resulting from the tissue layer simulations are presented in this paper.