Dose enhancement effects of different-sized nanoparticles on tumors and surrounding tissues using Geant4 track structure simulation

Free radicals, which are the most important contributors to cell death in radiotherapy, appear to increase in the presence of nanoparticles. The nanoparticles can be localized within tumor tissues, providing enhanced protection to normal tissues during radiation therapy while achieving significant dose enhancement within tumors. In our study, the dose effects of different sizes of spherical gold nanoparticles were analyzed in the tumor environment and surrounding tissues under photon radiation at various energies with the track structure code using the TOPAS interface. The nano-lattice method was used to create an environment similar to the diffusion-based distribution of nanoparticles in the medium. The Geant4-DNA code was utilized for simulations conducted in this study. Although the interaction cross-section is lower at MeV photon energy levels, the results still indicate an increase in dose due to the presence of nanoparticles (NPs) in the medium. As the size of gold nanoparticles increases, the spread in dose enhancements becomes more apparent. The lowest average dose enhancement factor (DEF) values at lateral points were observed for 28.4 nm NPs at MeV photon energy. In this study, the contribution of gold nanoparticles to dose enhancement was investigated using the Monte Carlo track structure algorithm. Additionally, the potential dose variations in the surrounding tissue resulting from the introduction of gold nanoparticles were analyzed. Even though an increase in DEF values was observed at MeV energy levels, these values might vary with a better understanding of biological effects such as cell cycle disruption, oxidative stress, and impaired DNA repair. This study offers valuable insights into nanoparticle-assisted radiation applications, including optimal nanoparticle size and applicable energy levels. By enhancing our understanding of the effects on tissues beyond the tumor and within the surrounding environment, it aims to provide critical information for researchers in the field and make a meaningful contribution to the literature.