Improvement of dose delivery with loading of tumor with gold nanoparticles in orthovoltage radiotherapy

Introduction: To enhance the dose to tumor, the use of high atomic number elements has been proposed. Objective: The aim of this study is to investigate the effect of gold nanoparticle distribution on dose enhancement in tumor when the tumor is irradiated by typical monoenergetic X-ray beams by considering homogeneous and inhomogeneous distributions of gold nanoparticles (GNPs) in the tumor.   Materials and Methods: Methods: MCNP-4C Monte Carlo code was utilized for the simulation of a source, a phantom containing tumor and gold nanoparticles with concentrations of 10, 30 and 70 mg Au/g tumor. A 15 cm ×15 cm ×15 cm cubic water phantom was irradiated with a small planar source with four monoenergetic X-ray beams of 35, 55, 75 and 95 kV energy. Furthermore, tumor depths of 2.5 cm, 4.5 cm and 6.5 cm with homogeneous and inhomogeneous distributions of GNPs were studied. Each concentration, photon energy, tumor depth and type of distribution was evaluated in a separate simulation. Results: Results have shown that dose enhancement factor (DEF) in tumor increases approximately linearly with the concentration of GNPs. While DEF has fluctuations with photon energy, 55 keV photons have the highest DEF values compared to other energies. While DEF has relatively the same values with tumor located at various depths, inhomogeneous distribution of GNPs has shown different results compared with the homogeneous model. Conclusion: Dose enhancement can be expected with tumors in radiotherapy with low energy X-rays. Inhomogeneous model is recommended for the purpose of dose enhancement study because it mimics the real distribution of GNPs in tumor.