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Browsing by Author "Leary, Del, advisor"

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    Evaluation of dose enhancement due to CuATSM uptake in hypoxic environments with external radiation
    (Colorado State University. Libraries, 2019) Martinez, Stephen K., author; Leary, Del, advisor; Boss, Keara, committee member; Brandl, Alexander, committee member; De Long, Susan, committee member; Kato, Takamitsu, committee member
    Most solid tumors contain areas of chronic hypoxia caused by limited diffusion of oxygen from tumor microvasculature. Hypoxic regions have been found to be radioresistant and their presence results in a worse prognosis for tumor control. Metal radiosensitizers have been employed to alleviate the radioresistance in hypoxic tumors by increasing dose through additional photoelectrons and Auger cascades. In recent years, gold nanoparticles (GNP) have been explored for their potential as an enhancer of external beam radiation and become the standard-bearer for the treatment modality; however, GNP have lower cellular uptake in anoxic and hypoxic conditions than under normoxic conditions. Additionally, the large size of nanoparticles decreases their diffusivity, reducing their ability to penetrate into tumor tissue distant from vasculature. The chelator diacetylbis (N(4)-methylthiosemicarbazonato) copper II (CuATSM) provides the potential to overcome the hypoxic barrier by preferentially depositing copper into tumor regions previously inaccessible to treatment. The characteristics of CuATSM have led to its utilization in positron emission tomography (PET) imaging of hypoxic regions. These PET images have also been investigated as a method for dose painting, amplification of intensity modulated radiation therapy (IMRT) dose to hypoxic regions. Additionally, radioactive ⁶⁴CuATSM has been investigated for implementation in brachytherapy for hypoxic tumors. The Auger electrons ejected upon decay of the radioisotope have been shown to be highly damaging to DNA. The intention of this study is to evaluate the potential of CuATSM as an external beam radiosensitizer. This project investigates radiosensitization of CuATSM by Monte Carlo (MC) modeling of different energy external beam spectra available clinically with Electron Gamma Shower (EGSnrc) and Geometry and Tracking (Geant4) and evaluating dose enhancement with CuATSM. These MC models are informed by and evaluated against cell models. Research indicates that CuATSM at high concentrations with low energy photons has efficacy for enhancing dose in hypoxic tumor regions.
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    Operational radiation safety considerations during superficial x-ray treatment for veterinary applications
    (Colorado State University. Libraries, 2021) Singh, Ashutosh, author; Leary, Del, advisor; Johnson, Thomas, advisor; Wotman, Kathryn, committee member
    This study was conducted to determine whether the scatter x-ray emission during a superficial radiation treatment (SRT) using the SRT-100™ result in a significant occupational dose to veterinary personnel present in the room during treatment. Measurements were taken for 50, 70, and 100 kV x-ray for 9 different SRT-100 applicators. The exposure rates at the surface of solid water phantom (SWP) phantom ranged from 3.9 mR/hr for applicator #2 to 396 mR/hr for CB18 for 50 kV, from 41 mR/hr to 2,880 mR/hr for 70 kV, and from 235 mR/hr to 7,500 mR/hr, for 100 kV, respectively. A heat map of scatter x-ray around the x-ray source was generated for 50, 70, and 100 kV at 25 cm and 75 cm above the SWP surface plane. The highest measured exposure rate was at 0.5 m from the applicator and was 76.8 mR/hr at 25 cm above SWP and 33.6 mR/hr at 75 cm above the SWP for 50 kV. Exposure rate values at same locations were 192 mR/hr and 96 mR/hr for 70 kV, and 389 mR/hr and 194 mR/hr for 100 kV, respectively. A horse phantom was utilized to generate a spatial dose profile at 1m for 50, 70, and 100 kV and it was discovered that backscatter emission has an angular response. Residence time for veterinary staff to exceed 10% of quarterly dose limits were calculated for 50, 70, and 100 kV and distances ranging from 0.5m to 2.5 m. These values ranged from a minimum of 24 min for 100 kV at 0.5m to a maximum of 7,813 min for 50 kV at 2.5 m. Minimum distance from the applicator for exposure rates below 2 mR/hr were calculated to be 1.78, 2.52, and 3.45 m, for 50, 70, and 100 kV, respectively.