Ronald C Walker

American Economic Association, United States

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Publications (12)39.89 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Multiple myeloma (MM) is an incurable plasma cell malignancy of the bone marrow. MM has 3 components: diffuse marrow infiltration, focal bone lesions, and soft-tissue (extramedullary) disease. The hallmark biomarker in blood or urine is a monoclonal immunoglobulin, the monoclonal protein. Waldenstrom macroglobulinemia is a similar disease with secretion of IgM. Staging is classically performed with the 1975 Durie-Salmon system, which includes conventional radiographs. Recently updated, the Durie-Salmon Plus staging system includes CT, MRI, and (18)F-FDG PET/CT. The hallmark radiographic lesion of symptomatic MM is a well-demarcated, focal osteolytic bone lesion. The number of focal bone lesions correlates inversely with outcome. Extramedullary disease is typically an aggressive, poorly differentiated form of MM that confers inferior outcome, with median survival of less than 1 y if present at diagnosis. Achievement of a complete response on (18)F-FDG PET before stem-cell transplantation correlates with a superior outcome.
    Journal of Nuclear Medicine 06/2012; 53(7):1091-101. · 5.77 Impact Factor
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    ABSTRACT: Pulmonary nodules often require operative resection to obtain a diagnosis. However, 10 to 30% of operations result in a benign diagnosis. Our purpose was to determine whether negative thoracic operations are futile by describing the pathological diagnoses; determining new diagnoses and treatment changes initiated based on operative findings; and assessing morbidity, mortality, and cost of the procedure. At our academic medical center, 278 thoracic operations were performed for known or suspected cancer between January 1, 2005, and April 1, 2009. We collected and summarized data pertaining to preoperative patient and nodule characteristics, pathologic diagnosis, postoperative treatment changes resulting from surgical resection, perioperative morbidity and mortality, and hospital charges for patients with benign pathology. Twenty-three percent (65/278) of patients who underwent surgical resection for a suspicious nodule had benign pathology. We report granulomatous disease in 57%, benign tumors in 15%, fibrosis in 12%, and autoimmune and vascular diseases in 9%. Definitive diagnosis or treatment changes occurred in 85% of cases. Surgical intervention led to a new diagnosis in 69%, treatment course changes in 68% of benign cases, medication changes in 38%, new consultation in 31%, definitive treatment in 9%, and underlying disease management in 34%. There was no intraoperative, in-hospital, or 30-day mortality. Postoperative in-hospital events occurred in seven patients. The mean total cost was $25,515 with a mean cost per day of $7618. Patients with a benign diagnosis after surgical resection for a pulmonary nodule received a new diagnosis or had a treatment course change in 85% of the cases.
    Journal of thoracic oncology: official publication of the International Association for the Study of Lung Cancer 07/2011; 6(10):1720-5. · 4.55 Impact Factor
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    ABSTRACT: The significance of medical imaging in multiple myeloma was established in 1975 with the classic description of the Durie–Salmon staging system which incorporated the presence and number of focal osteolytic lesions in the staging scheme. A third of a century later, this staging system remains in use, though augmented by advances in medical imaging. By the early 1980s, CT imaging demonstrated more focal bone lesions than were seen with standard radiographs as well as extramedullary disease. By the 1980s, MRI imaging revealed skeletal disease that was not apparent by either standard x-rays or CT, focal plasmacytomas in bone that had not yet produced focal osteolysis, and diffuse marrow infiltration. Subsequent work throughout the 1990s developed and established MRI as a very powerful tool to demonstrate the full extent of skeletal disease with resolution approaching a few millimeters. MRI was also used to direct biopsies of focal lesions which increased the detection rate of clinically relevant information compared to random marrow biopsies. However, standard MRI lacked the wide field of view of CT and was both considerably more expensive and less widely available than CT. An additional weakness of standard x-rays, CT, and MRI was their limited utility in the demonstration of response to treatment. By the mid- to late 1990s, the utility of 18F-FDG PET and (after 2000) PET/CT was apparent. PET/CT was particularly powerful since it provided a “whole-body” examination combining the utility of CT (“anatomy”) with a “metabolic” image that was linked to the Warburg physiology of tumors, at a fraction of the cost of an extensive MRI. Thus, PET and PET/CT can demonstrate both active disease and, very importantly, response to treatment. The PET image fused to the CT portion of the PET/CT also provides a “free” whole-body metastatic bone survey that can reveal not only focal bone lesions but also additional clinically relevant findings (fractures or impending fractures, additional malignancies, occult infections, unsuspected regions of tumor involvement such as extramedullary tumor). Recent work has established the fundamental importance of 18F-FDG PET and PET/CT for the baseline evaluation of patients with multiple myeloma and related plasma cell dyscrasias, as well as for subsequent evaluations related to patient management. Future directions for imaging research in multiple myeloma will include PET imaging with isotopes other than 18F-FDG and whole-body MRI. KeywordsImaging-MRI-PET-PET/CT-Skeletal survey-Focal lesion-Osteolytic lesion-Occult infection-DKK1-Extramedullary disease (EMD)
    04/2010: pages 15-62;
  • Aaron C. Jessop, Ronald C. Walker, Dominique Delbeke
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    ABSTRACT: Malignant cerebral tumors represent a small percentage (approximately 2%) of all malignancies, but have severe prognosis due to high morbidity and mortality. According to the American Cancer Society, in 2007 there were 23,300 new benign cerebral tumors and 20,500 new malignant cerebral tumors diagnosed in the United States, with an estimated number of resulting deaths of 12,760. Malignancies of the central nervous system (CNS) are the second most common malignancy in patients under the age of 20 (after hematologic malignancies) and are the leading cause of death from solid tumors in children and the third leading cause of death from cancer in the 15- to 34-year-old age group.
    12/2009: pages 99-135;
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    ABSTRACT: Infection imaging became widespread in 1971 with the release of 67Ga citrate. Multiphase skeletal scintigraphy and radiolabeled white blood cells (WBCs) have since become the most widespread clinically used agents for the imaging of infection. A wide variety of other radiolabeled probes are under investigation, based on antibodies, cytokines, assorted proteins and other molecules, alone or in various combinations. However, these latter agents, with a few exceptions, are not routinely used clinically. Radiolabeled ciprofloxacin represents the first attempt to develop an infection-specific imaging agent (most infection-imaging probes localized nonspecifically to inflammation as well), but it has not proven superior to radiolabeled WBCs or 18F-fluoro-deoxy-glucose (FDG) PET. Because of the ability to combine exquisite anatomic detail with focal uptake of 18F-FDG, PET-computed tomography has achieved great success in the detection and localization of infection, including in clinically adverse conditions. Despite these advances, at this time an infection-specific imaging agent does not exist.
    Future Microbiology 11/2007; 2(5):527-54. · 4.02 Impact Factor
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    ABSTRACT: To assess the prevalence, time of onset, risk factors, and outcome of avascular necrosis (AVN) of bone in patients with multiple myeloma undergoing antineoplastic therapy. A total of 553 consecutive assessable patients were enrolled onto a treatment protocol consisting of dexamethasone-containing induction chemotherapy, autologous stem-cell transplantation, consolidation chemotherapy, and maintenance with interferon alfa. Patients were randomly assigned to receive thalidomide (269 patients) or no thalidomide (284 patients) throughout the study period. With a median follow-up of 33 months (range, 5 to 114 months), AVN of the femoral head(s) developed in 49 patients (9%). Median time to onset of AVN was 12 months (range, 2 to 41 months). Three risk factors for AVN were identified by multivariate analysis: cumulative dexamethasone dose (odds ratio [OR], 1.028; 95% CI, 1.012 to 1.044; P = .0006 [per 40 mg dexamethasone]), male sex (OR, 0.390; 95% CI, 0.192 to 0.790; P = .009), and younger age (OR, 0.961; 95% CI, 0.934 to 0.991 per year; P = .0122). Thalidomide-treated patients had a prevalence of AVN similar to that of the control group (8% v 10%, respectively; P = .58). AVN-related pain and limited range of motion of the affected joint were present in only nine and four patients, respectively, and four patients underwent hip replacement because of AVN. Fluorine-18 fluorodeoxyglucose positron emission tomography failed to detect abnormal uptake in the AVN-affected bones. AVN is a rare and usually asymptomatic complication during myeloma therapy. Cumulative dexamethasone dose, male sex, and younger age, but not thalidomide, increase the risk of AVN.
    Journal of Clinical Oncology 09/2005; 23(22):5217-23. · 18.04 Impact Factor
  • Ronald C Walker
    IDrugs: the investigational drugs journal 04/2005; 8(3):189-92. · 2.33 Impact Factor
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    ABSTRACT: The aim of this study was to evaluate the role of [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging in the diagnosis of infection of implantable vascular catheters. We evaluated six patients with haematological cancer and infection of their implantable vascular catheter and who underwent FDG PET imaging around the time of their infection. Six patients with multiple myeloma who developed infection of their implantable device (five port pocket infections and one tunnel infection) were identified. FDG PET revealed increased uptake at the site of the implantable catheter (SUV 2.7-4.5) in all six patients, even in the absence of signs or symptoms of infection at the site of the device (three), and the presence of severe neutropenia (four). The three patients who did not have local inflammation at the site of the device were profoundly neutropenic. The FDG PET diagnosis led to removal of the device in two patients. FDG PET is a safe, rapid and accurate tool for diagnosing infection of an implantable catheter, including among those patients not exhibiting local signs and symptoms of infection, and in whom the diagnosis of infected device may be difficult. FDG PET may help prevent the unnecessary removal of implantable intravascular catheters and the unwarranted use of antibiotics.
    Nuclear Medicine Communications 09/2004; 25(8):813-8. · 1.38 Impact Factor
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    ABSTRACT: Medical imaging is migrating from anatomic imaging to functional imaging and fused anatomic/functional imaging. The technology is being adapted for biomedical research using both clinical and small animal scanners. The ability to externally image real-time physiologic processes in both normal and deranged conditions, including various models to image gene expression, apoptosis, or drug biodistribution, has powerful impact on the exploration of biomedical and fundamental biological research. Positron emission tomography (PET) has a unique ability to not only provide such images but also to do so with high resolution (typically 1-2mm resolution for small animal scanners) and to provide both relative and absolute quantitation. This technology is revolutionizing biomedical and biological research. This article reviews the underlying principles involved in this technology, gives a brief history of its development, and then introduces the interested researcher to some of the important techniques that could be of use.
    NeuroToxicology 07/2004; 25(4):533-42. · 2.65 Impact Factor
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    ABSTRACT: PET is one of the most exciting advancements in medicine in many years. Its ability to image physiology rather than anatomy, combined with the wide range of organic "probes" or molecules that can be utilized, offer remarkable possibilities for medical imaging in the coming years.
    The Journal of the Arkansas Medical Society 11/2002; 99(4):119-21.
  • Ronald C Walker, Steven S Zigler
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    ABSTRACT: PET systems, which are based on many years of work in theoretical and practical physics, provide a window into both normal and disease state biochemical processes not possible by other external imaging techniques. FDG is a workhorse of PET chemistry, helping to visualize the accumulation of glucose in cancer cells. A complex series of steps is involved in [18F]fluoride ion production to make a sterile, injectable solution of FDG. PET and CT scanners are being developed that increase greatly the clinical utility of both technologies.
    Journal of the American Pharmacists Association: JAPhA 43(5 Suppl 1):S42-3. · 1.16 Impact Factor
  • Dominique Delbeke, Ronald C. Walker
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    ABSTRACT: A variety of benign and malignant tumors occur in the liver. The most common benign hepatic tumors are cysts followed by cavernous hemangiomas. Focal nodular hyperplasia and adenomas more often affect women on oral contraceptives, whereas fatty infiltration and regenerating nodules more commonly occur in patients with cirrhosis. Abscesses and angiomyolipomas are uncommon. Among malignant tumors, metastases to the liver from various primaries, often multifocal, occur 20 times more often than primary hepatocellular carcinoma (HCC). Although many tumors may metastasize to the liver, this occurs mainly in colorectal, gastric, pancreatic, lung, and breast carcinoma. Ninety percent of malignant primary hepatic tumors are of epithelial origin and include HCC and cholangiocarcinoma.