Browsing by Subject "Radiation therapy"

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    A Deconvolution Formulation for Cerenkov Light Dosimetry in Radiation Therapy
    (2019-06) Brost, Eric
    Cerenkov light is the visible optical emission of photons that are created by the passage of high-energy charged particles in a dielectric medium. Since its discovery in 1934, Cerenkov light has been paramount to applications of high-energy radiation research. Recently, there has been considerable interest in imaging Cerenkov light during external beam radiation therapy as a means to perform in-vivo dose measurement. However, the exact relationship between Cerenkov light emission and dose deposition is not well characterized. In this thesis, the relationship between radiation beam fluence, dose deposition, and Cerenkov light emission is derived in an integral equation, describing the convolution relationships that exist between these physical parameters. This set of equations contained a convolution kernel called the Cerenkov scatter function (CSF). The CSF was solved with Monte Carlo techniques using the Geant4 architecture for medically-oriented simulations (GAMOS) to simulate radiation-induced optical emissions in an optical phantom and human skin tissue model. The theoretical formulation was experimentally evaluated using an optical phantom irradiated by high-energy photon beams. Next, the limitations and dependence of theoretical formulation were tested through a perturbation analysis performed on the CSF through Monte Carlo simulation. Lastly, the theoretical formulation was extended to clinically-relevant geometries, including curved surfaces, by breaking the limitation of space-invariance of the CSF. The theoretical formulation was found to improve the light-to-dose correspondence in Cerenkov light images, particularly in high dose gradient regions, and has the potential to improve the methods of Cerenkov imaging arising within radiation oncology. Based upon these results, it is expected that the theoretical formulation may be extended for use in a new Cerenkov imaging system which couples patient geometry imaging and measurement of Cerenkov light in-vivo.
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    Passive Wireless Radiation Dosimeters for Radiation Therapy Using Fully-Depleted Silicon-on-Insulator Devices
    (2017-01) Li, Yulong
    Radiation cancer therapy is one of the most important methods of cancer treatment. The goal of radiation therapy is to apply maximum amount of dose to the tumor region while applying minimum amount of dose to the normal tissues. Being able to measure radiation dose accurately is critical for radiation therapy because it will make sure the radiation is properly delivered to the tumor region as planned. In this dissertation, the development of a passive wireless radiation dosimeter for radiation cancer therapy based on fully-depleted silicon-on-insulator (FDSOI) technology was presented through the following steps. In Chapter 1, the radiation cancer therapy and existing dosimetry technology was introduced. Because of the high demand of modern radiation therapy and the deficiency of existing dosimetry. An ultra-small, passive radiation dosimeter will greatly help the dose verification in today’s radiation therapy. In Chapter 2, the building block of proposed dosimeter technology, FDSOI technology, was introduced and cutting edge development of FDSOI dosimeter was summarized. In Chapter 3, the radiation response of FDSOI metal–oxide–semiconductor field-effect transistors (MOSFETs) over a wide range of therapeutic X-ray beam energies, angles, dose ranges and applied substrate voltages were characterized. The charge collection efficiency was calculated from both technology computer aided design (TCAD) simulation and an analytical model to evaluate the radiation effect quantitatively. Based upon the experimental results, the design of passive wireless sensors using FDSOI varactors was proposed. In Chapter 4, the fabrication process of FDSOI varactors was developed at University of Minnesota. Capacitance vs. voltage (CV), current vs. voltage (IV), and TCAD modeling were used to fully understand the device characterization. The capacitance based sensing of Cobalt-60 (Co-60) gamma radiation was demonstrated using FDSOI varactors. An analytical model was developed to further understand the device response under irradiation. Based on the analytical model, the optimal working condition at different frequencies was discussed and a guide line of improving the device sensitivity was provided. TCAD simulation was also conducted to optimize the design space of FDSOI varactors for wireless sensing. In Chapter 5. 120-finger varactors with 0 V threshold voltage were fabricated using electron beam lithography with small device variability. An impedance measurement setup was built in clinical environment. Completely passive wireless radiation sensing was demonstrated using FDSOI varactor and the device showed good linearity of resonant frequency change under radiation. The possibilities to improve the performance of device were discussed. Chapter 6 summarized the progress of FDSOI dosimeter. The future development towards more reliable dosimeter with smaller sized was proposed. A novel device structure with two-dimensional material that could expend the application of solid-state radiation dosimeter was also proposed.