Utilisation of the chemiluminescence method to measure the radiation dose enhancement caused by gold nanoparticles: A phantom-based study

Abstract

Gold nanoparticles (AuNPs) are being investigated extensively for their role as radiosensitisers. Studies have shown that they are effective dose enhancing agents. One of the main factors that enables AuNPs to function as dose enhancing agents is their ability to generate reactive oxygen species under X-ray irradiation. In this study, we investigated this issue utilising a chemiluminescence technique with 3’-(p-aminophenyl) fluorescein (APF) in a phantom. First, we examined the time variation and dose response of the fluorescence intensity of APF for spherical 50 nm AuNPs exposed to a 6 MV photon beam. The APF reagent was added to the AuNPs suspension in a small tube fixed in a water phantom. The fluorescence intensities of APF were measured using a microplate reader. Next, based on the APF response, we evaluated the dose enhancements caused by AuNPs in a 6 MV flattening filter (FF) and flattening filter-free (FFF) photon beams and doses of either 2, 4, or 6 Gy. While the time variation of APF fluorescence intensity without AuNPs was less than 5% after X-ray irradiation, we observed an increase in the fluorescence intensity over time in the presence of AuNPs without the radiation. The APF signals had a linear response to X-ray irradiation in a dose-dependent manner. The measured dose enhancement ratios for the FFF beam were significantly higher than that for the FF beam in the presence of 30 μg/ml AuNPs. This result shows APF can successfully detect differences in dose enhancement between the FF and FFF beams using AuNPs. In conclusion, the chemiluminescence technique using APF is a useful and simple method to estimate the level of dose enhancement caused by nanoparticles in a phantom.