Radiation dose escalation by injecting bismuth, gold and platinum nanoparticles into a tumour during high dose rate 192Ir brachytherapy: a Monte Carlo study.

The purpose of this work was to determine and compare the dose enhancement of gold, platinum, and bismuth nanoparticles that were loaded into a tumour during high dose rate (HDR) brachytherapy. The Geant4 Monte Carlo toolkit was used to simulate an HDR ¹⁹²Ir radionuclide source. To verify the accuracy of the simulations, the obtained values of air-kerma strength, dose-rate constant (Λ), radial dose function, and 2D anisotropy function (F (r, θ)) were compared with the corresponding published values for the source used. The dose enhancement was computed by injecting 7, 18, and 30 mg/g concentrations of bismuth, platinum, and gold nanoparticles separately into a cube of 1 cm³ volume of the tumour placed in 20 × 20 × 20 cm³ of a soft tissue phantom. The absorbed dose to the tumour was quantified as a function of radial distance from the source centre and concentration of each nanoparticle by determining the dose enhancement factor. The dose enhancement factors in the tumour obtained in the presence of bismuth, gold, and platinum nanoparticles with a concentration of 30 mg/g were found to be 1.285, 1.266, and 1.231, respectively. However, beyond the tumour, at greater radial distances from the source centre, low dose enhancements were observed. Notwithstanding in vitro and in vivo studies, Bi NPs scored the highest dose enhancement due to the Bi mass attenuation coefficients in the tumour volume, with percentage dose enhancements up to 28.5% when used in HDR brachytherapy. Although in vitro and in vivo studies were not performed in the present study, it is concluded that for a similar source and concentration of nanoparticles, bismuth nanoparticles show higher dose enhancement than gold and platinum nanoparticles and may show a better clinical usefulness as dose enhancement materials.