Graduate Thesis Or Dissertation
 

Simulating the dose enhancement effects of platinum nanoparticles in a spherical geometry with Monte Carlo calculations

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k930c091v

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  • Background: The use of high-Z nanoparticles as radiation dose enhancers has been researched thoroughly over the past decade. High-Z nanoparticles introduced to a medium increase the probability of photoelectric absorption. This leads to an increase in the production of short range characteristic and Auger electrons and, thus, local radiation dose. These effects can be simulated by Monte Carlo codes. Materials and Methods: The EDKnrc user code of EGSnrc was used to simulate a simple spherical geometry. A 20 keV monoenergetic photon point source was positioned in the center of an air cavity sphere. A spherical shell composed of water-only or a concentration of platinum nanoparticle (PNP) in water the air cavity. A shell containing only water was placed around the outside. Simulations were run in the EGSnrc GUI on Microsoft Windows 10. Percent depth dose (PDDs) curves were calculated for each simulation. An additional simulation placing the concentration of PNPs in water at a different depth was used to investigate the accuracy of the code for interface effects for both low/high-Z and high/low-Z interfaces. Results: PDD curves in the zones containing some concentration of PNPs in water were to found attenuate faster than if the zone only contained water. There was a sudden drop in the PDD curves at the concentration of PNPs in water to the water-only interfaces for each simulation, which indicated a significant difference in the absorption of photons. The interface effects simulations showed a small increase in dose prior to the low/high-Z interface followed by a sharp drop in dose at the high/low-Z interface. Discussion: The faster attenuation in the simulations containing PNPs indicated that radiation was being absorbed more quickly than in the simulations containing only water. In addition, the sharp drop in PDD curves at the interfaces indicated that the outer water-only zone was being shielded by the PNP-water mixture zone. The interface effects simulations showed that the EGSnrc was accurately modelling the dose perturbations at the macro scale but was not as accurate in the micro scale. Conclusions: Although many simplifications were used in these simulations, the results may have some clinical significance. For example, intraoperative radiotherapy with an Intrabeam device uses a spherical geometry. Injection and distribution of PNPs prior to surgery could lead to large increases in radiation dose to the target volume while simultaneously shielding the non-target volume. More research is needed, which includes using more sophisticated codes and accurate modelling of PNP distribution in tissue, before PNPs can be used clinically.
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