A Monte Carlo study on tissue dose enhancement in brachytherapy: A comparison between gadolinium and gold nanoparticles

The aim of this study was to quantify the dose enhancement in presence of gadolinium nanoparticles (GdNPs) by Monte Carlo simulation and also a comparison between these results and dose enhancements by gold nanoparticles (GNPs). MCNPX Monte Carlo code was used to simulate in water brachytherapy sources: ⁶⁰Co, ¹⁹⁸Au, ¹⁹²Ir, ¹⁶⁹Yb. To verify the accuracy of our simulations, the values of dose rate constants and radial dose functions from this project were compared with corresponding published values for these sources. To study dose enhancements, a spherical soft tissue phantom with 15 cm in radius was simulated. Gadolinium and gold nanoparticles at 10, 20 and 30 mg/ml concentrations were assumed separately in a 1 cmx1 cmx 1 cm volume simulating tumor. The simulated dose to the tumor with the impurity was compared to the dose without impurity, as a function of radial distance and concentration of the impurity, to determine the enhancement of dose due to the presence of the impurity. Dose enhancements in the tumor obtained in the presence of gadolinium and gold nanoparticles with concentration of 30 mg/ml, were found to be in the range of 99.5%-206.1% and 100.4%-253.1% respectively. In addition, at higher radial distances from the source center, higher dose enhancements were observed. GdNPs can be used as a high atomic number material to enhance dose in tumor volume with dose enhancements up to 206.1% when used in brachytherapy. When comparing gadolinium and gold nanoparticles, for a similar source and concentration of nanoparticles, gold nanoparticles show higher dose enhancement. It is predicted that gold nanopartiocles can have more clinical usefulness as dose enhancer material when compared with gadolinium nanoparticles.