Browsing by Subject "Radiation"

Now showing 1 - 6 of 6
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    The addition of chemoradiation to lymph node positive gastric cancer is associated with improved overall survival
    (2019-07) Altman, Ariella
    Background: Adjuvant therapies improve survival in gastric cancer; however, the role of adjuvant chemoradiation in the treatment of lymph node (LN)-positive gastric cancer remains uncertain. This study sought to determine the role of adjuvant chemoradiation in addition to chemotherapy after resection for lymph node positive gastric cancer. Methods: The Surveillance, Epidemiology and End Results-Medicare linked data from 2004-2013 was used to identify patients aged 66 and older with LN-positive gastric adenocarcinoma. Multivariable logistic regression evaluated factors associated with receipt of chemoradiation. The Kaplan-Meier method and Cox proportional hazards modeling were used to evaluate overall survival (OS). Results: A total of 2,409 patients with LN-positive gastric adenocarcinoma who underwent upfront surgical resection were identified; 309 (13%) received adjuvant chemotherapy and 407 (17%) received adjuvant chemotherapy and chemoradiation. Among all patients, median OS was 15 months. Median OS was 20 months for patients who received chemotherapy alone and 27 months for patients who received chemotherapy and chemoradiation (p<0.05). Recent diagnosis, older age, tumor stage T3 or T4, and Charleston Comorbidity Index were associated with an increased hazard ratio for death (p<0.05). Receipt of chemoradiation was associated with a decreased hazard ratio for death (p<0.05). Conclusions: In patients with LN-positive gastric adenocarcinoma, the addition of chemoradiation to adjuvant chemotherapy after upfront surgical resection was associated with improved survival irrespective of the extent of lymphadenectomy. These data suggest chemoradiation should be considered in patients with LN-positive gastric adenocarcinoma.
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    CT Scans: What are the Risks?
    (2012-07-26) Zaban, Nick
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    Design and fabrication of state of the art uncooled thermopile infrared detectors with cavity coupled absorption
    (2013-06) Shea, Ryan Patrick
    We present the design, fabrication, and characterization of uncooled thermopile infrared detectors with cavity coupled absorption in the long wave infrared with performance exceeding all published works. These detectors consist of a two die optical cavity which enhances absorption in the desired spectral range while rejecting unwanted noise off resonance. The electrical transduction mechanism is a thermopile consisting of four thermoelectric junctions of co-sputtered Bi2Te3 and Sb2<\sub>Te3<\sub> having a room temperature unitless thermoelectric figure of merit of .43. Processing steps are described in detail for the fabrication of extremely thermally isolated structures necessary for highly sensitive detectors. Optical characterization of the devices reveals a responsivity of 4700 V/W, thermal time constant of 58 ms, and specific detectivity of at least 3.0x109<\super> cmHz1/2/W. Also presented are a theoretical proposal for a midwave infrared detector using semiconductor selective absorption to enhance detectivity beyond the blackbody radiation limit and a new method for the analysis of radiation thermal conduction in highly thermally isolated structures.
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    Impacts of SDF-1 and radiation dose-rate in an adult zebrafish model of hematopoietic cell transplant
    (2013-05) Glass, Tiffany
    Despite a history of refinements, Hematopoietic Cell Transplant (HCT) remains a potentially difficult treatment that can have high risks for complications and mortality. We used adult zebrafish models of HCT to study two broad biological processes that occur during HCT; homing and early donor-derived hematopoietic reconstitution. In the first case, we validated the adult zebrafish model for the study of the chemokine SDF-1 in HCT, developed a transgenic sdf-1 reporter zebrafish line, and used it to determine sites of high sdf-1 expression in recipient organisms. These sites were discovered both in the hematopoietic tissue as well as in previously un-described structures throughout the skin, and were found to consistently attract donor-derived cells after transplant. Ultimately, this allowed the identification of new putative HSC-niche cells which can be isolated with relative ease. Secondly, we assessed the effects of high conditioning radiation dose-rates on the process of hematopoietic engraftment after transplant. In groups of adult zebrafish given the same total dose of preconditioning radiation, we found that recipients irradiated at a high rate show significantly faster engraftment compared to those irradiated at a lower rate. Insights offered by this work will contribute to future efforts identifying endogenous factors promoting rapid engraftment, as well as to future reassessments of therapeutic opportunities offered by biologically informed refinements of preconditioning radiation strategies.
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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.
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    Transport and Chemical Phenomena in a Solar Thermochemical Reactor to Split Carbon Dioxide and Water to Produce Synthesis Gas
    (2015-10) Bala Chandran, Rohini
    Numerical study of a solar thermochemical reactor for isothermal reduction and oxidation of cerium dioxide is presented with the goal of accomplishing effective gas phase heat recovery and efficient gas utilization — the two most important attributes for achieving high fuel conversion efficiency in the reactor. Models were applied in tandem with and/or compared to experiments to interpret physical processes in the reactor and for validation. To achieve gas phase heat recuperation, a counterflow, ceramic heat exchanger filled with alumina reticulated porous ceramic was designed to operate at 1773 K. The focus of the modeling was selection of the morphology of the reticulated porous ceramic/ foam to balance heat transfer and pressure drop. Foam morphologies of 5–30 pores per inch (PPI) with porosities of 65–90% were considered. Large pore sizes, or equivalently low PPI, augment radiative penetration and reduce pressure drop. Solid phase conduction is the dominant mode of heat transfer over a majority of the heat exchanger length. Consequently, lower porosity improves the overall heat exchange at the penalty of increased pressure drop. The tradeoff in heat transfer performance and pressure drop point to use of higher porosity, 85–90%, and large pore sizes to optimize the solar-to-fuel efficiency. The final design is a 1.4 m long heat exchanger filled with 10 and 5 PPI, 85% porous, alumina foam in the annulus and center tube. This design recuperates more than 90% of the sensible energy of the reactant and product gases with less than 15 kPa pressure drop through the bed of ceria and heat exchanger. Motivated by the need to investigate the influence of transport processes on reactor performance, especially on the temperature distribution and the reaction rates, a transient, three-dimensional computational model of the reactor was developed. A hybrid Monte Carlo/finite volume approach was used to model radiative transport in the reactor surfaces and in the participating media. The chemical kinetics of the cyclic, gas-solid reactions were modeled by obtaining the best fit reaction rate coefficients from global rate data from a bench top reactor at 1773 K. For a solar input of 4.2 kW and gas flow rates of 0.67×10-4 mol s-1 gceria-1, the model predicts nearly isothermal cycling at an average temperature of 1791 K. Results elucidate that spatial variations in temperature, species concentration and reaction rate are interrelated and more pronounced along the gas flow direction. Carbon monoxide is produced continuously at 3.6×10-4 mol s-1, translating to 100 W of stored chemical energy. The overall reaction rates are driven by gas phase advection and the intrinsic material thermodynamics, rather than surface kinetics. The numerical modeling framework developed in this dissertation is robust and conducive to study other thermochemical processes in a high temperature solar reactor.