Microdosimetric Calculations for I-123 Using Geant4-DNA

Since early 1960s computational and mathematical models are used to describe complex biophysical processes associated with radiation induced cell death, as the earliest applications of molecular biology techniques to radiation biology. Most of these studies focuses on radioactive isotopes of iodine, particularly I-123, I-125 and exploring the potential of Auger electrons. From these studies it can be concluded as Auger electrons and Coster-Kronig (CK) electrons has LET value equivalent to heavy charged particles, which make them good candidate for targeted radiation therapy or tumor therapy using radioactive nanoparticles. Here, we have investigated various microdosimetric parameters for I-123 using GEANT4- DNA such as average energy deposited, S- value, and Dose Point Kernel (DPK) and compared them with literature. I-123 is used mainly in nuclear medicine because of its ideal γ-ray energy (159 keV) and relatively short half-life (13 .2 h). The decay of I-123 is, however, also associated with the production of Auger electrons (14% decay by Electron Capture). These low energy particles (< 500 eV) have a very short range in tissue (< 25 nm) (International Commission on Radiological Protection 1983) and as a result induce biological damage similar to that of high linear energy transfer radiations such as 5 MeV α-particles, provided that the isotope is allowed to decay within the cell nucleus. The main objective of this work is to reproduce the geometric model and results found on the H Fourie et al., 2014. This very first validation is as an exercise to learn the main features of GEANT4-DNA project and then go for more complex structures and simulations on the field of nanodosimetry.