title: Monte Carlo simulation of the RBE of I-131 radiation using DNA damage as biomarker.
abstract: In general, a weighting factor of one is applied for low linear energy transfer radiations. However, several studies indicate that relative biological effectiveness (RBE) of low energy photons and electrons is greater than one. The aim of this current study was calculating the RBE of I-131 radiation relative to Co-60 gamma photons in 100 μm spheroid cells using Monte Carlo (MC) simulations. These calculations were compared to experimentally measured results. MCNPX2.6 was used to simulate the I-131 and Co-60 irradiation setups and calculate the secondary electron spectra at energies higher than 1 keV with varying oxygen concentrations. The electron spectra at energies lower than 1 keV were obtained by extrapolation (down to 10 eV). The calculated electron spectra were input into the MCDS micro-dosimetric Monte Carlo code to calculate the DSB induction and related RBE. The calculated RBE of I-131 radiation relative to Co-60 photons, as the reference radiation recommended by the International Commission on Radiation Protection (ICRP), was 1.06, 1.03 and 1.02 for oxygen concentrations of 0, 5 and 100%, respectively. Results of MC simulations indicate the RBE of I-131 is greater than one. This finding, despite a 10% discrepancy with the findings of the previous in vitro study of one of the authors of this paper, reemphasizes that I-131 radiation induces more severe biological damage than current ICRP recommendations.
authors.affiliation: Faculty of Physics, University of Tabriz, Tabriz, Iran.
authors.forename: Ahad Ollah
authors.initials: AO
authors.lastname: Ezzati
authors.affiliation: The Persian Gulf Nuclear Medicine Research Center, Bushehr University of Medical Sciences, Bushehr, Iran. a.pashazadeh@bpums.ac.ir.
authors.forename: Ali
authors.initials: A
authors.lastname: Mahmoud-Pashazadeh
authors.affiliation: University of Miami, Miami, FL, USA.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Studenski
mesh_terms: D001610:Beta Particles; D015415:Biomarkers / Q000032:analysis*; D003037:Cobalt Radioisotopes / Q000737:chemistry; D003198:Computer Simulation; D004249:DNA Damage; D005720:Gamma Rays; D007457:Iodine Radioisotopes / Q000737:chemistry*; D009010:Monte Carlo Method; D012062:Relative Biological Effectiveness
chemical_list: D015415:Biomarkers; D003037:Cobalt Radioisotopes; D007457:Iodine Radioisotopes
keywords: Double-strand DNA breaks; I-131; Monte Carlo method; Radiation; Relative biological effectiveness