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Browsing by Author "Leary, Del, committee member"

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    ⁶⁴Cu-ATSM internal dosimetry in a computational tumor-bearing mouse model
    (Colorado State University. Libraries, 2021) Witter, Paige, author; Brandl, Alexander, advisor; Leary, Del, committee member; Stallones, Lorann, committee member
    The radiopharmaceutical Copper-64 diacetyl-bis(N4-methylthiosemicarbazones) (64Cu-ATSM) has growing clinical interest as a theragnostic agent; that is, one that can be used as both a diagnostic tool and a treatment for certain tumors. The ATSM ligand selectively distributes to hypoxic tissues, traditionally difficult targets for chemotherapy and radiotherapy cancer treatments. The copper radionuclide dissociates in the reducing environment, at which point the unique decay scheme of 64Cu offers multiple imaging and clinical pathways. Using an anatomically accurate voxelized phantom of a cancer-bearing mouse, a Monte Carlo N-Particle (MCNP) radiation transport code assessment of absorbed fractions and absorbed dose to major organs was carried out. In decay scenarios in which the organ of interest was the source organ, approximately 60% of the total energy transferred from a 64Cu decay came from the beta decay, approximately 30% from the positron decay, and approximately 1% from the Auger electrons. These results were used in conjunction with 64Cu-ATSM biodistribution data from two published studies to estimate organ and whole-body absorbed doses from administered activities. The differences in organ absorbed doses between the studies shows the mouse model variances that can impact dose and lead to variability in dose-response curves down the line. An MCNP model allows for a better understanding of the organ-specific doses and should be considered in the development of future studies assessing the theragnostic properties of 64Cu-ATSM in translational models while sparing these models' healthy organs and tissues.
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    Cytotoxicity, genotoxicity and DNA double-strand break repair mechanisms across the full carbon-ion beam range
    (Colorado State University. Libraries, 2021) Buglewicz, Dylan, author; Kato, Takamitsu, advisor; Legare, Marie, committee member; Sholders, Aaron, committee member; Leary, Del, committee member
    To view the abstract, please see the full text of the document.
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    Development of a decision threshold for radiological source detection utilizing Bayesian statistical techniques applied to gross count measurements
    (Colorado State University. Libraries, 2018) Brogan, John, author; Brandl, Alexander, advisor; Johnson, Thomas E., committee member; Leary, Del, committee member; Kokoszka, Piotr, committee member
    Numerous studies have been published using Bayesian statistics in source localization and identification, characterization of radioactive samples, and uncertainty analysis; but there is a limited amount of material specific to the development of a decision threshold for simple gross count measurements using Bayesian statistics. Radiation detection in low fidelity systems is customarily accomplished through the measurement of gross counts. Difficulties arise when applying decision techniques to low count rate data, which are restricted by the fact that decisions are being made on individual gross count measurements alone. The investigation presented demonstrates a method to develop a viable Bayesian model to detect radiological sources using gross count measurements in low fidelity systems. An integral component of the research is the process required to validate a Bayesian model both statistically and operationally in Health Physics. The results describe the necessary model development, validation steps, and application to the detection of radiological sources at low signal-to-background ratios by testing the model against laboratory data. The approach may serve as a guideline for a series of requirements to integrate Bayesian modeling (specifically, an interaction model) with radiation detection using gross counts in low fidelity systems.
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    Evaluating the genotoxic and cytotoxic effects of synthetic nucleosides in vitro
    (Colorado State University. Libraries, 2019) Haskins, Jeremy S., author; Kato, Takamitsu A., advisor; Leary, Del, committee member; Bouma, Gerrit, committee member
    The convoluted interplay between various cellular organelles has been a prominent area of study since humans have had the ability to research and explore the microscopic cellular world. Particularly, significant attention has been exercised in the effect that various compounds, pharmaceuticals, drugs, and therapies have on cellular division; particularly cancer cell division. Although documentation is scant, monitoring cell division has been of great interest for years. The utilization and administration of tritiated thymidine, to visualize cellular replication, was unarguably the first strategy to monitor cellular division. However, this method was deemed toxic and cumbersome. 5-bromo-2'-deoxyuridine (BrdU) soon took high notoriety. BrdU, a halogenated pyrimidine, and its structurally related analogs are known to mimic the deoxynucleoside, thymidine, during S-phase of cellular replication. BrdU is incorporated in place of thymidine during S-phase, and its rate of incorporation can be monitored via immunohistochemical antibody detection. However, current literature has demonstrated that BrdU presents a number of complications regarding long-term labeling, cell cycle progression, cellular mutagenicity and cytotoxicity, and unwanted photosensitivity. BrdU's shortcomings were bypassed by the advent of 5-ethynyl-2'-deoxyuridine (EdU) (25). EdU, an additional synthetic analog of thymidine, having a terminal 5'-ethynyl- substituent, instead of thymidine's or BrdU's terminal 5'-methyl- or 5'-bromo- substituent, respectively. EdU has gained popularity as the preferred method in detecting cellular division due to its inherent ability to readily incorporate into newly synthesized DNA. In order to detect and incorporate BrdU into DNA, the process requires the expenditure of an antibody. Binding of the BrdU-antibody tandem to DNA necessitates denaturation of DNA via volatile acid or heat treatment, which presents complications as unqualified and unfaithful base-paring and reannealing. Conversely, EdU incorporation and detection is a fast, simple, and effective method in labeling actively dividing cells. By way of "click" chemistry, EdU is readily introduced and synthesized into new DNA. The latter is accomplished, in part by a small-sized fluorescent azide, qualifying easy access to DNA without considerable steric hindrance. It is expected that successful incorporation of EdU, via "click" chemistry will result in high resolution microscopy analysis. However, current research suggests that implementation of EdU may result in unwanted biological effects. Using an in vitro system, the experimental basis described herein sought to determine the effects that BrdU or EdU had on cell cytotoxicity and genotoxicity when incorporated in DNA. Whilst a vast majority of research experiments use concentrations of said nucleosides' in the range of 10-50 µM, these conditions may induce strong genotoxic and cytotoxic effects inherently higher than the expected background frequency. By treating various DNA repair deficient cells with BrdU or EdU, at concentrations ranging from 1-100 µM, there was a significant increase in the induction of sister chromatid exchanges. Also, with identical concentrations as the latter, the doubling time of particular DNA repair deficient cell lines increased dramatically. To examine the effects of BrdU and EdU on DNA repair, a poly (ADP ribose) polymerase (PARP) ELISA assay was carried out. The PARP assay concluded that BrdU possessed the highest degree of PARP inhibition, with thymidine second, and EdU with the least PARP inhibition. One suggested mechanism by which BrdU is thought to implicate or hinder DNA repair is through its incorporation and modification of DNA repair thus, slower repair kinetics. Hypoxanthine-guanine phosphoribosyltransferase (HPRT) mutation analysis suggests that manufacturers recommended EdU concentration (10µM), result in a significantly higher HPRT mutation frequency, compared to control. In addition to BrdU's SCE-induction capability and HPRT-induction incidence, clinical and radiotherapeutic properties have been examined. CHO cells exposed to 2 and 8 µM BrdU and 4 or 15 Gy X-rays, increase DNA repair duration, increased chromosomal fragmentation, and induce radiosensitization. However, little or no evidence is available in regard to EdU's propensity to affect cell viability. To assess the induction of cellular radiosensitivity and chromosomal aberrations, we investigated CHO and A549 (human lung cancer) cells replicative ability in the presence of three external radiation. An in vitro clonogenic and chromosomal aberration assay, in the presence of UVC-, photon (fluorescent)-, and γ-irradiation and BrdU or EdU, was implemented. Our results support BrdU's ability to decrease cell viability. Although each synthetic analogue presented their own biological contribution, their mechanism is still not fully understood. This study aims to discern any cytotoxic and/or genotoxic effects that EdU or BrdU pose on cell cycle progression, clonogenicity and viability, mutation-induction, chromosomal aberrations, and induction of radiosensitization.
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    Improved detection of radioactive material using a series of measurements
    (Colorado State University. Libraries, 2016) Mann, Jenelle, author; Brandl, Alexander, advisor; Johnson, Thomas, committee member; Kokoszka, Piotr, committee member; Leary, Del, committee member
    The goal of this project is to develop improved algorithms for detection of radioactive sources that have low signal compared to background. The detection of low signal sources is of interest in national security applications where the source may have weak ionizing radiation emissions, is heavily shielded, or the counting time is short (such as portal monitoring). Traditionally to distinguish signal from background the decision threshold (y*) is calculated by taking a long background count and limiting the false negative error (α error) to 5%. Some problems with this method include: background is constantly changing due to natural environmental fluctuations and large amounts of data are being taken as the detector continuously scans that are not utilized. Rather than looking at a single measurement, this work investigates looking at a series of N measurements and develops an appropriate decision threshold for exceeding the decision threshold n times in a series of N. This methodology is investigated for a rectangular, triangular, sinusoidal, Poisson, and Gaussian distribution.
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    Internal dosimetric evaluation of Cu-64-ATSM in canine cancer bearing patients
    (Colorado State University. Libraries, 2015) Bell, Justin James, author; Brandl, Alexander, advisor; Jones, Brian, committee member; Leary, Del, committee member
    The assessment of the novel radiopharmaceutical Copper-64 diacetyl-bis(N4-methylthiosemicarbazones) (64Cu-ATSMs) ability to selectively accumulate in hypoxic tumor tissue has been subject to ongoing research effort at Colorado State Universitie's (CSU) Veterinary Teaching Hospital (VTH). Due to the unique decay scheme of 64Cu and internal distribution when bound to ATSM, the radiopharmaceutical has clinical importance as a possible Positron Emission Tomography/Computed Tomography (PET/CT) imaging agent with cancer theranostic potential. In this study, the PET/CT images of two cancer bearing canine patients treated with 64Cu-ATSM were used to create patient specific voxelized phantoms that were compatible with the Monte Carlo N Particle extended (MCNPX) radiation transport code which was emplyed to retrospectively assess the internal radiation dose each patient received. By defining specific regions of interest (ROI) within the models, the dose to major organs was estimated. The derived models were designed as to dynamically approximate the relative dose each patient would receive to their tumor and normal tissue if the administered activity of 64Cu-ATSM was altered. From these results, it was identified that the patient's malignances received 64Cu-ATSM uptake at least during the acquisition of the patients' images. Organs such as the liver also had relatively high amounts of 64Cu-ATSM uptake and were used to project what ROI might be dose limiting.
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    Investigation of clinical gastrointestinal toxicity and underlying normal tissue damage associated with concurrent abdominal radiation therapy and tyrosine kinase inhibition
    (Colorado State University. Libraries, 2023) Prebble, Amber R., author; Boss, Mary-Keara, advisor; LaRue, Susan, committee member; Leary, Del, committee member; Thamm, Douglas, committee member
    Tyrosine kinase inhibitors (TKIs) may be combined with radiation therapy (RT) to enhance tumor control due to their anticancer and antiangiogenic effects; however, clinical evidence has emerged which suggests the treatment combination of RT and TKI may result in higher incidence of normal tissue side effects, dependent on the organs at risk in the radiation treatment field, than would be expected for either modality alone. We evaluated the incidence of gastrointestinal (GI) toxicity in canine cancer patients receiving concurrent hypofractionated abdominal RT and the TKI toceranib and compared to those receiving abdominal RT alone, toceranib alone, or concurrent non-abdominal RT and toceranib. Medical records of canine cancer patients were retrospectively reviewed and identified dogs were included in the following treatment categories: dogs which received RT to a portion of the abdomen and concurrent TOC (n = 19), abdominal RT alone (n = 29), TOC alone (n = 20), or non-abdominal RT plus TOC (n = 9). Toxicities were graded using the Veterinary Cooperative Oncology Group - Common Terminology Criteria for Adverse Events criteria and compared to published data on TOC-associated GI toxicity. Patients receiving TOC while undergoing abdominal RT had significantly increased rates of any grade of diarrhea (p = 0.002), hyporexia (p = 0.0045), and vomiting (p = 0.003), as well as severe hyporexia (p = 0.003) when compared across the treatment groups. This retrospective study revealed significantly increased incidences of GI toxicity when abdominal RT was combined with TOC in canine patients. Following these findings, we investigated the morbidity and underlying histological changes associated with combined abdominal RT and the TKI sunitinib in a mouse model. Prior to the experimental study, we identified a dose of abdominal RT in CD1 outbred mice which would induce mild GI toxicity according to weight loss and histologic changes in GI tissues harvested 7 days after irradiation; 12 gray (Gy) was selected as the optimal dose for the subsequent experiment. Twenty-five mice were then assigned to control (n = 5), sunitinib alone (n = 7), RT alone (n = 6), or RT + sunitinib (n = 7) groups and were weighed daily. All mice received daily oral gavage of vehicle or sunitinib (40 mg/kg) in vehicle for the entire study. On day 7 mice received 12 Gy abdominal RT or sham irradiation. On day 14 mice were euthanized and their entire GI tract was harvested for histopathologic evaluation, semiquantitative scoring of inflammation, and immunohistochemical quantification of cells positive for CD31 (vascularity) and Ki67 (proliferation). Major findings of this study included that mice in the combined therapy group, RT + sunitinib, lost significantly more weight than sunitinib alone (p < 0.0001) or RT alone (p = 0.0258). Mice in the RT alone group had a significant increase in GI vascular density, as determined by CD31, when compared to the SUN group (p = 0.0252). The mice in the RT + sunitinib group did not mount the same GI vascular response as the RT treated mice. The RT + sunitinib group had more crypt abscessation when compared to groups not receiving RT (vs. Control, p = 0.0076; vs. sunitinib alone, p = 0.0023). And, while it did not reach statistical significance when compared to the RT alone group, the RT + sunitinib group had more abscessation than RT alone (p = 0.0862) which could indicate a trend of higher levels of crypt abscessation with this combined treatment modality. The results from our canine retrospective clinical study and the preclinical mouse model experiment suggest that abdominal RT + TKI increases morbidity and GI toxicity at the RT and TKI doses investigated. Continued investigation of the underlying normal tissue effects associated with concurrent TKI and abdominal RT are recommended in order to determine whether combining these therapies could be optimized for safety and efficacy, such that GI toxicity is minimalized while achieving optimal tumor control.