Physics Commons^™

Post-Modeling Adjustments And Delivered Dose Verification Of The 6fff Beam Model Commissioned For The Monaco Treatment Planning System, Grant C. Debevec

LSU Master's Theses

External beam radiation therapy has been shown to be an effective treatment method for tumors and abnormalities of the spine and vertebral region. Treating the spine using a stereotactic body radiation therapy (SBRT) technique can reduce toxicity to the spinal cord. The 6 MV flattening filter free (6FFF) beam model is currently used to plan and calculate dose for SBRT treatment plans, and the treatment plans are delivered using a linear accelerator (LINAC).

The commissioned beam model represents an invariant component of a LINAC. For volumetric modulated arc therapy (VMAT) treatment plans, the multileaf collimator (MLC) positions are changing throughout …

Experiments And Data Analysis For Modulated Phase Gratings In X-Rays, Sydney B. Carr

LSU Master's Theses

Purpose: Modulated Phase Grating (MPG) interferometry has been shown in theory and simulations to produce observable fringes on a clinical detector without requiring fluence absorbing analyzer. In this work, we will experimentally show that the MPG X-ray system produces observable fringes and multi-modal X-ray images.

Motivation:Nearly 1 in 8 women in the US will develop invasive breast cancer in their lifetime, accounting for approximately 40,000 deaths each year [1-2]. In order to pursue the best treatment option available, cancer itself must be adequately imaged and staged, based on size and level of metastasis, on the order of Stage I-IV. …

Hybrid Modulated-Phase-Grating For Phase Contrast X-Ray For A Varying Fringe Period Clinical Interferometry System, Elizabeth Jeong Park

LSU Master's Theses

Phase contrast x-rays are of use due to the range of imaging they can provide. Not only are they useful for attenuation they also can provide phase and small angle scatter X-ray (SAXS) information simultaneously which adds additional contrast and information to the original attention image. In prior work, a phase contrast system with Modulated Phase Grating was shown to eliminate the need for analyzer in standard Talbot Lau Xray Interferometers (TLXI). The system is clinically compatible in footprint due to its length being limited to

Accident Simulation Study For Nuclear Power Plants Impacting Louisiana, Michael D. Mcmahon

LSU Master's Theses

INTRODUCTION: Louisiana has aligned its radiological emergency program with the 2017 Environmental Protection Agency Protective Action Guides Manual, but has added a child thyroid dose evacuation threshold in lieu of distributing Potassium Iodide to the public. The nuclear power plants will continue to align with the 1992 manual for the foreseeable future, so that under some accident scenarios the state recommendations will differ from those of the utility.

OBJECTIVE: The objective of this study is to predict what accident and weather conditions will lead to a differing set of recommendations.

METHODS: More than 1000 simulations were performed of low-filtration nuclear …

In-Phantom Film Measurements Of Two Treatment Planning Systems For Single-Fraction Spine Sbrt, Michael J. Taylor

LSU Master's Theses

Purpose: Treatment planning accuracy for spine stereotactic body radiation therapy (SBRT) varies depending on the dose calculation algorithm utilized in the treatment planning system (TPS). This project compared the end-to-end accuracy between spine SBRT plans calculated in a convolution-superposition based TPS (TPS_CS) and Monte Carlo based TPS (TPS_MC) with radiochromic film measurements. The hypothesis was that TPS_MC would calculate the dose gradient in the critical region between the vertebral body and the spinal cord more accurately than TPS_CS.

Methods: Single-fraction spine SBRT treatments following RTOG 0631 and local institutional guidelines were planned in …

Structural Shielding Considerations For Vmat, Ana Lucia Dieguez

LSU Master's Theses

Introduction: As noted in National Council on Radiation Protection and Measurements (NCRP) Report 151, the medical physicist or other qualified expert has the responsibility to keep abreast of any new technology or treatment method that could potentially impact structural shielding design. Volumetric arc therapy (VMAT) became prevalent after the publication of Report 151 and thus was not explicitly addressed in Report 151. If the shielding-related characteristics of VMAT differ enough from the expectations of Report 151, especially in the circumstance of a vault utilized exclusively for VMAT, a shielding design based on Report 151 could potentially be inadequate. The …

Visualization Of Brown Fat Using X-Ray Dark Field Imaging, Troy D. Jacobs

LSU Master's Theses

Introduction: Obesity has become a major societal issue. Many researchers are looking for ways to combat this growing epidemic. Brown adipose tissue (BAT) might be a way to help individuals overcome the challenges associated with weight loss and maintenance of weight loss, but a better understanding of BAT and how to control and utilize it is needed. BAT differs from white adipose tissue (WAT) in that BAT is rich with mitochondria and therefore is metabolically active. BAT is a source of non-shivering thermogenesis and can be activated both by cold exposure and pharmacologically. Current methods of assessing BAT activity are …

Analytical Setup Margin For Spinal Sbrt Based On Measured Errors, Audrey Copeland

LSU Master's Theses

Purpose: No consensus currently exists in the radiotherapy community about the correct margin size to use for spinal SBRT. Margins have been proposed to account for various errors individually, but not with all errors combined to result in a single margin value. The purpose of this work was to determine a setup margin for spinal SBRT based on known and measurable errors during radiotherapy to achieve at least 90% coverage of the clinical target volume (CTV) with the prescription dose for at least 90% of patients and not exceed a 30 Gy point dose or 23 Gy to 10% of …

Evaluation Of Neutron Skyshine Contributions During Injection At An Electron Synchrotron Facility Using Fluka, Andrew D. Hastings

LSU Master's Theses

The Center for Advanced Microstructures and Devices (CAMD) is a 1.5 giga-electron volt (GeV) electron synchrotron research facility under the jurisdiction of Louisiana State University (LSU). When originally constructed in 1992, CAMD was surrounded by pasture and woodland. Over the past several years, urban development of the area has found CAMD bracketed by a shopping center, apartment complex, and business offices. These developments raised concerns amongst the CAMD radiation safety personnel regarding an increased potential for public exposure to radiation. To ensure compliance with the annual public effective dose equivalent limit of 1 milli-sievert (mSv), the radiation monitoring program was …

Visualization And Quantitation Of Radioiodine Distribution In Silver Zeolite Cartridges, Daniel Dimarco

LSU Master's Theses

Iodine 131 is a major fission product released during a nuclear incident. This isotope provides a serious health hazard for humans and the environment, therefore nuclear power plants must monitor releases using air sampling. The air sampling is accomplished using air filter cartridges using silver zeolite as a filter media. During an emergency situation, silver zeolite is useful for its affinity to I-131 without adsorbing other radioactive gases. After leaving the plume, these cartridges are counted in a low background area. This measurement does not take into account the distribution of radioiodine in the cartridge. This study explores two methods …

Assessment Of Excess Thyroid Cancer Risk Following A Hypothetical Radiological Incident In Louisiana And Best-Case Risk Reduction Achieved By Thyroid Blockade, Garrett A. Otis

LSU Master's Theses

Radioactive isotopes of iodine are produced by nuclear power plants as a byproduct of nuclear fission reactions. If these isotopes are released into the environment, such as during a breach of containment, they constitute a health risk to exposed individuals. To mitigate the risk of thyroid cancer due to exposure to radioactive iodine, “iodide prophylaxis,” also known as “thyroid blockade,” can be used, usually by administration of potassium iodide (KI). In some areas of the world, KI has been provided to the general public by their governments as a precautionary measure against potential nuclear power plant incidents. However, in the …

Determination Of Scatter Fractions, Albedos, And Tenth Value Layers For Shielding Of Synchrotron Beamline Hutches, Bethany Lynn Broekhoven

LSU Master's Theses

Synchrotron facilities require substantial amounts of shielding to protect facility staff and researchers. To meet mandatory exposure limits, the traditional combination of time, distance, and shielding of the radiation source are utilized. Because of continuous 24-7 operation of most synchrotrons, time is the least useful tool. The experimental stations for synchrotron x-ray beamlines, called hutches, enforce a minimum distance from the source, but shielding provided by hutch walls is still the principal tool for a synchrotron facility. Currently there is no single resource for synchrotron beamline hutch shielding design in the literature; most hutch shielding is designed through either over-simplified …

Evaluation Of Ventilation Assistance For Improving Respiratory Reproducibility In Radiation Therapy, Cameron J. Sprowls

LSU Master's Theses

Background: Respiratory motion affects all tumor sites in the thorax and abdomen. Variations of the respiratory pattern cause variations of the tumor motion which can result in differences between the planned and delivered dose distributions. Previous breathing guidance techniques have been investigated to improve respiratory reproducibility; however, ventilation assistance has not been investigated. We evaluated using bi-level positive airway pressure (BIPAP) ventilation assistance for improving respiratory reproducibility in patients with tumor sites impacted by respiratory motion.

Methods: Written informed consent was obtained for 10 patients currently undergoing radiation therapy treatment. Patients participated in sessions over their course of treatment, which …

Determination Of Conversion Factors For Various Calibration Geometries Using Barium-133 In A Silver Zeolite Cartridge, Amin Hamideh

LSU Master's Theses

Iodine-131 (I-131) is a major fission product among other radionuclides released during a nuclear incident. This radioiodine has a half-life of 8.02 days and the primary organ of uptake through ingestion or inhalation is the thyroid gland. For these reasons, nuclear power plants must routinely monitor I-131 through air sampling. Currently, there are two adsorbing media to collect I-131: activated charcoal and silver zeolite cartridges. Silver zeolite cartridges are generally used during a post nuclear incident due to its affinity for iodine while not adsorbing noble gases such as krypton-85 and xenon-135. After an air sample is taken from a …

Third Generation Gamma Camera Spect System, Narayan Bhusal

LSU Master's Theses

Single Photon Emission Computed Tomography (SPECT) is a non-invasive imaging modality, frequently used in myocardial perfusion imaging. The biggest challenges facing the majority of clinical SPECT systems are low sensitivity, poor resolution, and the relatively high radiation dose to the patient. New generation systems (GE Discovery, DSPECT) dedicated to cardiac imaging improve sensitivity by a factor of 5-8. The purpose of this work is to investigate a new gamma camera design with 21 hemi-ellipsoid detectors each with a pinhole collimator for Cardiac SPECT for further improvement in sensitivity, resolution, imaging time, and radiation dose.

To evaluate the resolution of our …

Analytical Models Of Neutron Spectral Fluence, Kerma And Absorbed-Dose For Proton Therapy, Suman Shrestha

LSU Master's Theses

Abstract

Purpose: The accurate prediction of stray neutron dose has become increasingly important as it increases the risk of second cancer development after proton therapy. Previously reported analytical models predicted the quantity dose equivalent, which includes physical and biological considerations but does not explicitly take into account material dependence and variation in the radiation quality. The purpose of this study was to investigate the feasibility of an analytical model of absorbed dose to water from stray neutrons in proton therapy.

Methods: To calculate neutron absorbed dose and kerma in water, the authors developed analytical models of neutron spectral fluence and …

Verification And Evaluation Of A Passive Intensity Modulation Device For Bolus Conformal Therapy, Elizabeth Noel Hilliard

LSU Master's Theses

Purpose: Bolus electron conformal therapy (BECT) provides effective radiation treatment for superficial cancers and other diseases close to the skin surface, but can have as great as a 30% planning target volume (PTV) dose heterogeneity due to scattering from the irregular proximal bolus surface. Intensity modulated (IM) BECT can improve PTV dose homogeneity, but is not currently available. This study fabricated patient-specific passive intensity modulators and validated their delivering planned dose distributions calculated by a modified pencil beam redefinition algorithm (PBRA).

Methods: Two test-patterns and four patient-specific intensity modulators were designed, fabricated, and tested. Dose plans were generated …

Benefit Of Intensity Modulated Bolus Electron Conformal Therapy For Post Mastectomy Chest Wall Irradiation, John Doiron

LSU Master's Theses

Purpose: The delivery of post-mastectomy radiotherapy (PMRT) with bolus electron conformal therapy (BECT) for patients with left-sided breast cancer can reduce second cancer complication probability (SCCP) compared to modern rotational intensity modulated x-ray (IMXT) techniques such as volumetric modulated arc therapy (VMAT) or Tomotherapy. However, rotational IMXT yields superior levels of dose homogeneity compared to BECT. This study investigates the use of intensity modulated (IM) BECT (IM-BECT) to improve dose homogeneity in the chest wall (CW) region of the PMRT planning target volume (PTV) abutted to parallel opposed IMXT tangents for the remaining PTV for a clinically-representative set of patients, …