Purpose: The current study was designed to calculate the dose enhancement factor (DEF) of iodine (I), gold (Au), bismuth (Bi), gadolinium (Gd), and hafnium (Hf) nanoparticles (NP)s by Monte Carlo (MC) modeling of an electronic brachytherapy source in resection cavities of breast tumors.
Methods and materials: The GEANT4 MC code was used for simulation of a phantom containing a water-filled balloon and a Xoft source (50 kVp) to irradiate the margins of a resected breast tumor. NPs with a diameter of 20 nm and concentrations from 1 to 5% w/w were simulated in a tumor margin with 5 mm thickness as well as a hypothetical breast model consisting of spherical island-like residual tumor-remnants. The DEFs for all NPs were calculated in both models.
Results: In the margin-loaded model, for the concentration of 1% w/w heavy atom, DEFs of 2.5, 2.3, 2.1, 2, and 1.7 were calculated for Bi, Au, I, Hf, and Gd NPs (descending order), which increased, almost linearly with concentration for all NPs. Moreover, normal tissue dose behind the NP-loaded margin declined significantly depending on NP type and concentration. When modeling residual tumor islands, DEF values were very close to the margin-loaded values except for Bi and I, where DEFs of 2.55 and 1.7 were seen, respectively.
Conclusions: Considerable dose enhancements were obtained for the heavy atom NPs studied in the partial breast brachytherapy with a Xoft electronic source. In addition, normal tissue doses were lowered in the points beyond the NP-loaded margin. The findings revealed promising outcomes and the probability of improved tumor control for NP-aided brachytherapy with the Xoft electronic source.
Keywords: Brachytherapy; Breast cancer; Dose enhancement; Nanoparticle; Xoft.
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