Browsing by Author "Tourassi, Georgia D"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Accuracy and Patient Dose in Neutron Stimulated Emission Computed Tomography for Diagnosis of Liver Iron Overload: Simulations in GEANT4
    (2007-08-13) Kapadia, Anuj
    Neutron stimulated emission computed tomography (NSECT) is being proposed as an experimental technique to diagnose iron overload in patients. Proof-of-concept experiments have suggested that NSECT may have potential to make a non-invasive diagnosis of iron overload in a clinical system. The technique's sensitivity to high concentrations of iron combined with tomographic acquisition ability gives it a unique advantage over other competing modalities. While early experiments have demonstrated the efficacy of detecting samples with high concentrations of iron, a tomography application for patient diagnosis has never been tested. As with any other tomography system, the performance of NSECT will depend greatly on the acquisition parameters that are used to scan the patient. In order to determine the best acquisition geometry for a clinical system, it is important to evaluate and understand the effects of varying each individual acquisition parameter on the accuracy of the reconstructed image. This research work proposes to use Monte-Carlo simulations to optimize a clinical NSECT system for iron overload diagnosis.Simulations of two NSECT systems have been designed in GEANT4, a spectroscopy system to detect uniform concentrations of iron in the liver, and a tomography system to detect non-uniform iron overload. Each system has been used to scan simulated samples of both disease models in humans to determine the best scanning strategy for each. The optimal scanning strategy is defined as the combination of parameters that provides maximum accuracy with minimum radiation dose. Evaluation of accuracy is performed through ROC analysis of the reconstructed spectrums and images. For the spectroscopy system, the optimal acquisition geometry is defined in terms of the number of neutrons required to detect a clinically relevant concentration of iron. For the tomography system, the optimal scanning strategy is defined in terms of the number of neutrons and the number of spatial and angular translation steps used during acquisition. Patient dose for each simulated system is calculated by measuring the energy deposited by the neutron beam in the liver and surrounding body tissue. Simulation results indicate that both scanning systems can detect wet iron concentrations of 5 mg/g or higher. Spectroscopic scanning with sufficient accuracy is possible with 1 million neutrons per scan, corresponding to a patient dose of 0.02 mSv. Tomographic scanning requires 8 angles that sample the image matrix at 1 cm projection intervals with 4 million neutrons per projection, which corresponds to a total body dose of 0.56 mSv. The research performed for this dissertation has two important outcomes. First, it demonstrates that NSECT has the clinical potential for iron overload diagnosis in patients. Second, it provides a validated simulation of the NSECT system which can be used to guide future development and experimental implementation of the technique.
  • Thumbnail Image
    ItemOpen Access
    Development and Design of a Near-Field High-Energy Gamma Camera for Use with Neutron Stimulated Emission Computed Tomography
    (2007-12-10) Sharma, Amy Congdon
    A new gamma imaging method, Neutron Stimulated Emission Computed Tomography (NSECT), is being developed to non-invasively and non-destructively measure and image elemental concentrations in vivo. In NSECT a beam of fast neutrons (3 - 5 MeV) bombards a target, inelastically scattering with target nuclei and exciting them. Decay from this excited state produces characteristic gamma emissions. Collecting the resulting gamma energy spectrum allows identification of elements present in the target. As these gamma rays range in energy from 0.3 - 1.5 MeV, outside the useable energy range for existing gamma cameras (0.1 - .511 MeV), a new gamma imaging method must be developed. The purpose of this dissertation is to design and develop a near-field (less then 0.5 m) high-energy (0.3 - 1.5 MeV) gamma camera to facilitate planar NSECT imaging. Modifying a design implemented in space-based imaging (focus of infinity), a prototype camera was built. Experimental testing showed that the far-field space-based assumptions were inapplicable in the near-field. A new mathematical model was developed to describe the modulation behavior in the near-field. Additionally, a Monte Carlo simulation of the camera and imaging environment was developed. These two tools were used to facilitate optimization of the camera parameters. Simulated data was then used to reconstruct images for both small animal and human fields of view. Limitations of the camera design were identified and quantified. Image analysis demonstrated that the camera has the potential to identify regions of interest in a human field of view.
  • Thumbnail Image
    ItemOpen Access
    Knowledge-based IMRT treatment planning for prostate cancer.
    (2011) Chanyavanich, Vorakarn
    The goal of intensity-modulated radiation therapy (IMRT) treatment plan optimization is to produce a cumulative dose distribution that satisfies both the dose prescription and the normal tissue dose constraints. The typical manual treatment planning process is iterative, time consuming, and highly dependent on the skill and experience of the planner. We have addressed this problem by developing a knowledge based approach that utilizes a database of prior plans to leverage the planning expertise of physicians and physicists at our institution. We developed a case-similarity algorithm that uses mutual information to identify a similar matched case for a given query case, and various treatment parameters from the matched case are then adapted to derive new treatment plans that are patient specific. We used 10 randomly selected cases matched against a knowledge base of 100 cases to demonstrate that new, clinically acceptable IMRT treatment plans can be developed. This approach substantially reduced planning time by skipping all but the last few iterations of the optimization process. Additionally, we established a simple metric based on the areas under the curve (AUC) of the dose volume histogram (DVH), specifically for the planning target volume (PTV), rectum, and bladder. This plan quality metric was used to successfully rank order the plan quality of a collection of knowledgebased plans. Further, we used 100 pre-optimized plans (20 query x 5 matches) to show that the average normalized MI score can be used as a surrogate of overall plan quality. Plans of lower pre-optimized plan quality tended to improve substantially after optimization, though its final plan quality did not improve to the same level as a plan that has a higher pre-optimized plan quality to begin with. Optimization usually improved PTV coverage slightly while providing substantial dose sparing for both bladder and rectum of 12.4% and 9.1% respectively. Lastly, we developed new treatment plans for cases selected from an outside institution matched against our sitespecific database. The knowledge-based plans are very comparable to the original manual plan, providing adequate PTV coverage as well as substantial improvement in dose sparing to the rectum and bladder. In conclusion, we found that a site-specific database of prior plans can be effectively used to design new treatment plans for our own institution as well as outside cases. Specifically, knowledge-based plans can provide clinically acceptable planning target volume coverage and clinically acceptable dose sparing to the rectum and bladder. This approach has been demonstrated to improve the efficiency of the treatment planning process, and may potentially improve the quality of patient care by enabling more consistent treatment planning across institutions.