Abstract

Different kinds of nanoparticles have been widely studied for biomedical purposes, including applications like dose enhancement in radiotherapy treatments and contrast agent in radiological studies. Recent work suggests that gold nanoparticles can be used as contrast agents in K-edge imaging and X-ray Fluorescence Computed Tomography, mainly due to their high K-edge energy value and good biocompatibility. However, the gold X-ray fluorescence (XRF) signal obtained in these procedures is relatively week when compared with Compton or bremsstrahlung radiation emitted in the surrounding tissues, mainly because it is not possible to achieve large gold nanoparticles concentrations within biological tissues added to the XRF is attenuated by other tissues when leaving the patient body. This work presents a feasibility study on implementation of FLUKA, PENELOPE and MCNP6 Monte Carlo codes to model the detection of gold XRF emitted by a small volume containing different gold concentrations and located at different depths in a tissue-equivalent phantom. Results indicate that there is good agreement between PENELOPE and FLUKA for gold K alpha and K beta lines estimations when highly symmetric simulation scenario and kilovoltage X-ray beam were used, achieving differences lower than 2%; however, differences up to 6 times were observed between FLUKA and MCNP6 under the same conditions. In addition, remarkable differences were obtained when megavoltage X-ray beam was used, being up to 11 times between PENELOPE and FLUKA and up to 4 times between FLUKA and MCNP6 for gold K alpha and K beta lines estimations. In this regard, a suitable normalization method was proposed and implemented to perform cross-comparisons of XRF estimations obtained from the Monte Carlo codes. By means of the proposed method, FLUKA, PENELOPE and MCNP6 can be successfully implemented to assess which configuration (gold concentration and target volume depth) leads to a better detection of gold XRF, despite differences in XRF estimation between the codes.