TU-C-BRB-11: In Vitro Dose Enhancement from Gold Nanoparticles under Different Clinical MV Photon Beam Configurations
Purpose: To quantify the relative in vitro dose enhancement due to the presence of goldnanoparticles (GNPs) in a clinical 6 MV beam. It is expected that depths and delivery modes that produce larger proportions of low energy photons will have a larger effect on cell samples containing GNP. Methods: HeLa cells were combined with 50 nm GNPs at a concentration of 0 or 0.05 mg/ml. The cells were irradiated in clinical solid water at depths of 1.5, 5, 10, 15 and 20 cm (SAD setup). Conventional beams with square aperture sizes 5, 10 and 15 cm at isocenter, IMRT and flattening filter free (FFF) beams were used. DNA double strand breaks (DSBs) were evaluated by H2AX staining. Results: Statistically significant dose enhancement was observed for all depths and delivery modes. Dose enhancement ratios varied between 1.1 and 1.7. Relative to the shallowest depth, dose enhancement was observed to increase as a function of increasing depth for all deliveries. For the conventional (open field) delivery, dose enhancement was seen to increase as a function of field size. The IMRT delivery chosen for this study did not significantly increase the dose enhancement at each depth, but did in the aggregate. For FFF delivery, a substantial increase in gH2AX foci was found, relative to the conventional field delivery. Without GNP, no enhancement was observed as a function of depth, indicating that the enhancing effect with GNP is due to the change in energy spectrum under each delivery condition. Conclusions: The measured relative dose enhancement validates the theoretically predicted trends in dose enhancement as a function of depth and delivery mode for a clinical MV beam. The results of this study open new possibilities for the clinical development of goldnanoparticle aided radiation therapy.