1. (DPD 09) Physics 2: EXPERIMENTAL EVALUATION OF FREE RADICAL GENERATION IN NANOPARTICLE-AIDED HDR BRACHYTHERAPY 1,3 Nava Paudel, 1 Diana Shvydka, 2 Eric Findsen, and 1 E. Ishmael Parsai 1 Department of Radiation Oncology, 2 Department of Chemistry, The University of Toledo, Toledo, OH 3 University of Arkansas for Medical Sciences, Little Rock, AR ‎

2. Background High atomic number materials in tumor enhance radiation dose deposition through the generation of secondary electrons Extensively studied with Monte Carlo (MC) simulations, showing very low enhancement ratios for MV energies – Evaluate enhancement in energy deposition (dose) There are reports of cell kill in biological experiments higher than the predictions based on pure radiation dose deposition We aim at unraveling the controversy between the physical dose enhancement and resulting biological effects

3. Approach Free radicals – Major mediators producing cell damage in low LET radiation – Hydroxyl radical is the dominant one We measure free radicals generated by gold and platinum micro-wires in water, placed in capillaries (1.2 mm diameter) Use electron paramagnetic resonance (EPR) Compare radical generation enhancements under Ir-192 source with MC modeled dose enhancements

4. Take Home Points Experimentally obtained enhancements of OH radical generation due to Au/Pt in aqueous medium are – Higher than those attributable to dose deposition for thin wires – Equal to dose enhancement ratios for thick wires Diameter (μm) MC modeled DE (%) due to Au/Pt OH enhancement (%) due to AuPt 1008 ± 317 ± 4- 12711 ± 328 ± 529 ± 7 25020 ± 521 ± 519 ± 3 50027 ± 723 ± 422 ± 5 Possibly, due to higher surface to volume ratios for thin wires: metal interface could play a role of secondary source of free radicals NPs-aided radiation therapy could be practical even for MV energies This effect should be responsible for cell damages higher than predicted based on MC results