Determination of dose enhancement caused by AuNPs with Xoft(®) Axxent(®) Electronic (eBx™) and conventional brachytherapy: in vitro study

PURPOSE: The purpose of this study was to determine dose enhancement (DE) and the possible clinical benefits associated with the inclusion of gold nanoparticles (AuNPs) in cancer cells irradiated by either an (192)Ir brachytherapy source or a Xoft(®) Axxent(®) Electronic (eBx™) Brachytherapy. PATIENTS AND METHODS: Brachytherapy DE caused by AuNPs is investigated using two methods, namely (192)Ir and eBx™ Brachytherapy. The second method, which was recently introduced clinically, operates at ~50 kV, which is also the optimal beam energy for DE. In this in vitro study, two cancer cell lines, lung (A549) and prostate (DU145), were used. Cells were incubated with 1 mM (2% w/w) concentration of AuNPs of ~15 nm in size. The control groups were exposed to a range of doses from 0 (control) to 6 Gy, with eBx™ and (192)Ir sources separately. A clonogenic assay was conducted to determine cell survival curves. RESULTS: High dose enhancement factor (DEF) values were achieved in treated groups with low concentration of AuNPs with the 50 kV energy associated with the eBx™. The DE levels in eBx™ for Du145 and A549 cells were found to be 2.90 and 2.06, respectively. The results showed DEFs measured for the same cell lines using (192)Ir brachytherapy to be 1.67 and 1.54 for Du145 and A549 cancer cells, respectively. This clearly indicates that much higher DE values are obtained in the case of eBx™ X-ray brachytherapy compared to (192)Ir gamma brachytherapy. CONCLUSION: The higher DE values obtained with eBx™ compared to (192)Ir brachytherapy can be attributed to the lower average energy of the former and being closer to the optimal energy for DE. This could potentially be utilized by medical practitioners and clinicians to achieve the same tumor control with a significantly lower dose from the eBx™ compared to the (192)Ir brachytherapy treatment, thus bringing huge benefits to the brachytherapy-treated patients.