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Title:Effective dose enhancement using gold as a radiation sensitizer: a Monte Carlo study
Author(s):Ahmed, Nabeel G.
Advisor(s):Ragheb, Magdi
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Effective dose enhancement using AuNP
Monte Carlo simulations for effective dose enhancement
Abstract:Despite years of research, a significant gap remains between the cancer burden requiring treatment and the mechanisms currently available in clinical settings. Although great strides have been made in improving radiation therapy, the issue of non-specific irradiation of healthy tissue still persists. One of the most promising modalities currently being explored involves using contrast material to enhance the radiation sensitivity of a tumor. Such treatment aims to create a gradient in the photon attenuation coefficients of the tumor compared to those of the surrounding healthy tissue. The goal of generating such a variation is to dramatically increase the amount of effective dose received by the tumor without increasing the amount received by the surrounding healthy tissue. Several contrast materials have been explored for this application with iodine and gadolinium receiving generating significant interest. Following the promising results achieved by utilizing gold nanospheres in murine models, interest in gold has correspondingly increased. This work examines several variables as they might pertain to the effectiveness of using gold as a radiation-sensitizing agent. Physical considerations involving the incident photon energy, geometric considerations involving the depth of the tumor, and concentration considerations involving the amount and distribution of gold around the tumor site have all been explored. Results were tabulated by comparing the amount of energy deposited per unit mass in the gold-bearing tumor volume compared to the surrounding healthy tissue and this ratio was termed the effective dose enhancement factor (DEF). Using a gold concentration of 7 mg per kg of tumor resulted in DEF values ranging from 62%, when a 100 keV photon beam was modeled, to less than 1%, when applying a 2 MeV photon beam. Varying the depth of tumor had less effect than expected as increasing the depth from 5 cm to 15 cm only increased the effective dose enhancement from 16% to 19% when using a 250 keV photon beam. Varying the in situ gold concentration had the most significant effect as expected and DEF values increased by a factor of four from 18% to 76% as concentration was increased from 7 mg/kg to 40 mg/kg. The results obtained from using a more detailed geometric and concentration model and considering realistic distribution patterns may be of use when designing future in vivo studies. The results of the distribution and penetration models may be used to predict the effective dose profiles for tumor masses that are resistant to nanoparticle influx. Monte Carlo simulations were developed using Cartesian geometry and all material specifications and gold concentration data were obtained from the literature. Tissue and tumor were treated as homogeneous mixtures of their component elements, and gold nanoparticles were modeled as homogenous distributions where specified. Flux and energy deposition calculations were performed using Monte Carlo N-Particle Code version 5.1.51.
Issue Date:2011-08-25
Rights Information:Copyright 2011 Nabeel G. Ahmed
Date Available in IDEALS:2011-08-25
Date Deposited:2011-08

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