Graduate Thesis Or Dissertation

An investigation into the feasibility of neutron activating holmium-loaded, polymeric microspheres in the thermal column of a TRIGA reactor using MCNP5 simulation models

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  • In intra-arterial radioembolization, nano- and micro-scaled carriers are used in patients with liver tumors that cannot be removed by surgery to deliver various radioisotopes with the aim of improving the outcome of tumor radiotherapy, of minimizing dose to healthy tissue, and of improving the quality of the diagnosis and imaging. In this technique, radioisotopes are incorporated in either nanospheres or microspheres for delivery. The synthesis of these maybe performed either using the isotope in its radioactive form or nonradioative form; however, if the synthesis is performed using non-radioactive isotopes, a subsequent activation by neutron bombardment in a nuclear reactor is required. This investigation focused on neutron-activation simulations using computer models of microspheres loaded with holmium acetylacetonate (HoAcAc) complex in a polymeric matrix that are used for intra-arerial radioembolization therapy of liver cancer. The polymer matrix is made of poly (L-lactic acid) (PLLA) which is both biodegradable and biocompatible. In addition, as a requirement for therapeutic applications of these microspheres, not only their diameter must be within a range between 20 and 50 micrometers, but also before administration to a patient, they must be neutron-activated by turning holmium-165 into holmium-166. The main objective of this investigation was to minimize the energy deposited by neutrons and gammas produced by fission and neutron activation reactions that would result in damages to both the microsphere's polymeric matrix and holmium complex. To accomplish this objective, Monte Carlo N-Particle models were created to perform the following simulations: (1) microspheres loaded with a HoAcAc complex in a polymeric matrix were exposed to a neutron flux in the thermal column of a TRIGA reactor while arranged in a sheet-shaped packing configuration, and, similarly, (2) while arranged in a pile-shaped packing configuration, microspheres also loaded with a HoAcAc complex in a polymeric matrix were also exposed to the same neutron flux in the thermal column. Then, results from both types of simulations were analyzed and were compared.
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