Analysis of physical dose enhancement in nano-scale for nanoparticle-based radiation therapy: a Cluster and endothelial cell model

One major difficulty of conventional radiotherapy is the lack of selectivity between the tumor and the organs at risk. In nanoparticle aided radiotherapy, heavy elements are present at higher concentrations in the tumor than normal tissues. This study aimed to model the characteristics of secondary electrons generated from the interaction of clusters comprised of five different nanoparticles including Gold, Gadolinium, Iridium, Bismuth, and Hafnium atoms with low energy x-rays (similar to brachytherapy sources in terms of energy) as a function of nanoparticle size and beam energy. To better evaluate the contributions of secondary electrons in energy deposition, and also to develop a framework in analyzing further measurements in the future, we attempted to enhance and promote existing mathematical models for energy deposition in endothelial cells by nanoparticle-enhanced radiotherapy. Also, the MCNPX Monte Carlo code was used to model the identical geometry and the dose enhancement factor was calculated for all types of simulated nano-clusters. Our results showed that for our model consist of a nano-cluster and an endothelial cell the DEF significantly depends on the energy of photons and L- and K-edge binding energy of the atoms inside the nano-cluster. However, for Gd at the energy 60 keV, a higher dose enhancement factor was seen. It can be concluded that the mathematical model considers the DEF variation with photon energy and the effect of NP type is considered in DEF calculations. However, the MC method has indicated very high sensitivity to photon energy, and NP type compared to the mathematical method.