Investigation of a dose-enhancement factor of Nano-Gadolinium contrast agent by Monte Carlo simulation

Nowadays, the use of nanoparticles has made many developments to enhance the effectiveness of radiotherapy. Many parameters such as size, concentration, type, and intracellular position of nanoparticles, as well as type and energy of the radiation source, affect the sensitivity. In this study, the effect of the presence of gadolinium in the cell has been investigated, and the role of these physical parameters has been evaluated in the dose-enhancement factor (DEF). Using Geant4 software, different distributions of gadolinium nanoparticles (GdNP) and gadolinium atoms were simulated inside a cell. The sources of low energy (25 keV- 80 keV) and high energy from linear electron accelerator (Eave =2 MeV) were irradiated to a single cell, and the dose was obtained in its membrane cytoplasm, and the nucleus was calculated. Then, the effect of its size and X-ray source energy on the DEF value was investigated by simulating a nanoparticle. At the cellular scale, a rapid increase in DEF occurred after the Gd K-edge. The lowest DEF is in the core. The maximum DEF belongs to the distribution of Gd atoms in the cytoplasm and the distribution of Gd nanoparticles in the membrane with the values of 1.20 and 1.17 at 52 keV, respectively. At 2 MeV, the DEF in all distributions is close to 1. At the nanoscale, it was also found that the highest DEF was related to nanoparticles with a radius of 50 nm. Also, the DEF value increases sharply after the Gd K-edge, but at 2 MeV, the DEF value approaches 1.