Medical Biophysics Commons^™

Scanned Ion Beam Therapy For Thoracic Tumors, John Gordon Eley

Dissertations and Theses (Open Access)

Although frequently cured of Hodgkin lymphoma, adolescents and young adults can develop radiation induced second cancers. These patients could potentially benefit from scanned ion radiotherapy yet likely would require motion mitigation strategies. In theory, four-dimensional (4D) optimization of ion beam fields for individual motion states of respiration can enable superior sparing of healthy tissue near moving targets, compared to other motion mitigation strategies. Furthermore, carbon-ion therapy can sometimes provide greater relative biological effectiveness (RBE) for cell sterilization in a target but nearly equivalent RBE in tissue upstream of the target, compared to proton therapy. Thus, we expected that for some …

Investigation Of Respiratory Motion Management Techniques For Proton And Photon Radiotherapy Of Lung Cancer, Jason E. Matney

Dissertations and Theses (Open Access)

Protons as a source of therapeutic radiation can provide a substantial improvement over dose distributions that can be achieved with conventional sources of radiation such as high-energy photons. However, respiratory motion can significantly impact the delivered proton and photon dose distributions during lung cancer radiotherapy. The goals of this dissertation research were to evaluate the impact of respiratory motion and to estimate the benefit of respiratory gating for passively scattered proton therapy (PSPT) and intensity modulated photon therapy (IMRT).

The first aim of this project was to determine the impact of respiratory motion in PSPT and IMRT. Four dimensional dose …

Evaluation Of Presage® Dosimeters For Brachytherapy Sources And The 3d Dosimetry And Characterization Of The New Agx100 125i Seed Model, Olivia Huang

Dissertations and Theses (Open Access)

With continuous new improvements in brachytherapy source designs and techniques, method of 3D dosimetry for treatment dose verifications would better ensure accurate patient radiotherapy treatment. This study was aimed to first evaluate the 3D dose distributions of the low-dose rate (LDR) Amersham 6711 Oncoseed^TM using PRESAGE^® dosimeters to establish PRESAGE^® as a suitable brachytherapy dosimeter. The new AgX100 ¹²⁵I seed model (Theragenics Corporation) was then characterized using PRESAGE^® following the TG-43 protocol.

PRESAGE^® dosimeters are solid, polyurethane-based, 3D dosimeters doped with radiochromic leuco dyes that produce a linear optical density response to radiation dose. …

Improving Cervical Cancer Nodal Boost Radiation Therapy By Quantifying Uncertainties And Exploring Advanced Radiation Therapy Modalities, Zhiqian Yu

Dissertations and Theses (Open Access)

Radiation therapy for patients with intact cervical cancer is frequently delivered using primary external beam radiation therapy (EBRT) followed by two fractions of intracavitary brachytherapy (ICBT). Although the tumor is the primary radiation target, controlling microscopic disease in the lymph nodes is just as critical to patient treatment outcome. In patients where gross lymphadenopathy is discovered, an extra EBRT boost course is delivered between the two ICBT fractions. Since the nodal boost is an addendum to primary EBRT and ICBT, the prescription and delivery must be performed considering previously delivered dose. This project aims to address the major issues of …

Development Of A Beam-Specific Planning Target Volume And A Robust Plan Analysis To Ol For Proton Therapy, Peter Park

Dissertations and Theses (Open Access)

Proton therapy is growing increasingly popular due to its superior dose characteristics compared to conventional photon therapy. Protons travel a finite range in the patient body and stop, thereby delivering no dose beyond their range. However, because the range of a proton beam is heavily dependent on the tissue density along its beam path, uncertainties in patient setup position and inherent range calculation can degrade thedose distribution significantly. Despite these challenges that are unique to proton therapy, current management of the uncertainties during treatment planning of proton therapy has been similar to that of conventional photon therapy. The goal of …

Improved Techniques For Acquisition And Analysis Of Dynamic Contrast-Enhanced Magnetic Resonance Imaging For Detecting Vascular Permeability In The Central Nervous System, Cheukkai Hui

Dissertations and Theses (Open Access)

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a noninvasive technique for quantitative assessment of the integrity of blood-brain barrier and blood-spinal cord barrier (BSCB) in the presence of central nervous system pathologies. However, the results of DCE-MRI show substantial variability. The high variability can be caused by a number of factors including inaccurate T1 estimation, insufficient temporal resolution and poor contrast-to-noise ratio. My thesis work is to develop improved methods to reduce the variability of DCE-MRI results. To obtain fast and accurate T1 map, the Look-Locker acquisition technique was implemented with a novel and truly centric k-space segmentation scheme. In …

In-Vivo Ct Dosimetry During Virtual Colonoscopy, Jonathon W. Mueller

Dissertations and Theses (Open Access)

Virtual colonoscopy (VC) is a minimally invasive means for identifying colorectal polyps and colorectal lesions by insufflating a patient’s bowel, applying contrast agent via rectal catheter, and performing multi-detector computed tomography (MDCT) scans. The technique is recommended for colonic health screening by the American Cancer Society but not funded by the Centers for Medicare and Medicaid Services (CMS) partially because of potential risks from radiation exposure. To date, no in‐vivo organ dose measurements have been performed for MDCT scans; thus, the accuracy of any current dose estimates is currently unknown.

In this study, two TLDs were affixed to the inner …

Risk Of Second Malignant Neoplasms Following Proton Arc Therapy And Volumetric Modulated Arc Therapy For Prostate Cancer, Laura A. Rechner

Dissertations and Theses (Open Access)

The risk of second malignant neoplasms (SMNs) following prostate radiotherapy is a concern due to the large population of survivors and decreasing age at diagnosis. It is known that parallel-opposed beam proton therapy carries a lower risk than photon IMRT. However, a comparison of SMN risk following proton and photon arc therapies has not previously been reported. The purpose of this study was to predict the ratio of excess relative risk (RRR) of SMN incidence following proton arc therapy to that after volumetric modulated arc therapy (VMAT). Additionally, we investigated the impact of margin size and the effect …

New To Ols For Monitoring Gamma Camera Uniformity, Brad K. Lofton

Dissertations and Theses (Open Access)

Detector uniformity is a fundamental performance characteristic of all modern gamma camera systems, and ensuring a stable, uniform detector response is critical for maintaining clinical images that are free of artifact. For these reasons, the assessment of detector uniformity is one of the most common activities associated with a successful clinical quality assurance program in gamma camera imaging. The evaluation of this parameter, however, is often unclear because it is highly dependent upon acquisition conditions, reviewer expertise, and the application of somewhat arbitrary limits that do not characterize the spatial location of the non-uniformities. Furthermore, as the goal of any …

Volumetric Modulated Arc Therapy Evaluation With The Radiological Physics Center Head And Neck Phantom, Kelly Kisling

Dissertations and Theses (Open Access)

Validation of treatment plan quality and dose calculation accuracy is essential for new radiotherapy techniques, including volumetric modulated arc therapy (VMAT). VMAT delivers intensity modulated radiotherapy treatments while simultaneously rotating the gantry, adding an additional level of complexity to both the dose calculation and delivery of VMAT treatments compared to static gantry IMRT. The purpose of this project was to compare two VMAT systems, Elekta VMAT and Varian RapidArc, to the current standard of care, IMRT, in terms of both treatment plan quality and dosimetric delivery accuracy using the Radiological Physics Center (RPC) head and neck (H&N) phantom. Clinically relevant …

Measurement Of The Vascular Input Function In Mice For Dce-Mri, Dustin K. Ragan

Dissertations and Theses (Open Access)

DCE-MRI is an important technique in the study of small animal cancer models because its sensitivity to vascular changes opens the possibility of quantitative assessment of early therapeutic response. However, extraction of physiologically descriptive parameters from DCE-MRI data relies upon measurement of the vascular input function (VIF), which represents the contrast agent concentration time course in the blood plasma. This is difficult in small animal models due to artifacts associated with partial volume, inflow enhancement, and the limited temporal resolution achievable with MR imaging. In this work, the development of a suite of techniques for high temporal resolution, artifact resistant …

Thoracic Radiotherapy Treatment Planning With Cine Pet/Ct, Adam C. Riegel

Dissertations and Theses (Open Access)

Purpose: Respiratory motion causes substantial uncertainty in radiotherapy treatment planning. Four-dimensional computed tomography (4D-CT) is a useful tool to image tumor motion during normal respiration. Treatment margins can be reduced by targeting the motion path of the tumor. The expense and complexity of 4D-CT, however, may be cost-prohibitive at some facilities. We developed an image processing technique to produce images from cine CT that contain significant motion information without 4D-CT. The purpose of this work was to compare cine CT and 4D-CT for the purposes of target delineation and dose calculation, and to explore the role of PET in target …