Evaluation of dose enhancement in presence of gold nanoparticles in eye brachytherapy by 103Pd source.

In recent years, the use of gold nanoparticles in radiation therapy has been introduced as a new approach in radiotherapy. The aim of this study is to investigate the effect of gold nanoparticles (GNPs) in plaque brachytherapy for choroidal melanoma using Monte Carlo (MC) simulation. MCNPX code was used for simulation of human eye, 103Pd (model 200) brachytherapy source and the 20 mm COMS eye plaque that was loaded with 24 103Pd seeds and standardized by Collaborative Ocular Melanoma Study (COMS). The tumour was defined from the inner surface of choroid with 0.55 cm height and latticed with gold nanospheres and it was filled with different concentrations of 5, 10 and 15 mg/g GNPs, separately. Dose rate and dose enhancement factor in tumour and normal tissues of the eye (without gold) was examined for this case and compared with gold-water mixture of the same concentrations distributed in the tumour. The results show that with increasing the concentration of GNPs, the dose in the tumour increases and the dose to the normal tissues decreases. Furthermore, the time that is required to deliver the prescribed dose to the tumour decreases. In the gold nanosphere case for 5, 10 and 15 mg/g concentrations, the DEF in the apex of the tumour are 1.28, 1.46, 1.44 and at the distance of 6.5 mm in the normal tissue (outside the tumour) this factor would be 0.82, 0.73 and 0.68. The comparison between two cases of gold nanospheres and gold-water mixture shows that when the gold concentrations are defined as mixed with water, the dose enhancement in the first depths are higher than when the gold-nanoparticles are distributed inside the tumour. Furthermore due to more reduced particle flux for water-mixture case, by an increase in the depth the dose enhancement in gold-nanosphere increases compared with gold-water mixture case.