<p>Yttrium-90 (<sup>90</sup>Y) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). In treatment planning, reliable prediction of the 90Y distribution <i>in vivo</i> is essential to performing both safe and effective therapy. However, the distribution of surrogate agents used in treatment planning may not exactly predict the distribution of <sup>90</sup>Y. Thus it would be useful to image the <sup>90</sup>Y distribution after therapeutic administration to provide the ground truth for the <sup>90</sup>Y distribution. This would facilitate evaluating and potentially improving pre-therapy methods for individualizing and optimizing the therapy. Single photon emission computed tomography (SPECT) is a powerful imaging technique for estimating 3D distribution of radionuclides <i> in vivo.</i> However, as an essentially pure β-particle emitter, <sup> 90</sup>Y does not emit gamma photons considered appropriate for SPECT imaging. One possible solution is to image bremsstrahlung photons generated by the interaction of the 13-particles with atomic nuclei in the body. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes substantial challenges on quantitative SPECT imaging. The overall goal of this work was to develop and evaluate new quantitative bremsstrahlung SPECT methods for improving the reliability (accuracy and precision) of the <sup> 90</sup>Y activity estimates for the dosimetry application. </p><p> Reconstruction method, acquisition energy window, and collimator are three crucial factors that determine the reliability of quantitative SPECT imaging. </p><p> In this work, we first developed an improved quantitative reconstruction method. The improvement resulted from more accurate modeling of the image formation process in a statistical iterative reconstruction method. Improvements in the model included enhancements to the Monte Carlo (MC) bremsstrahlung simulation used to generate various components of the model and better modeling of the energy dependence of various image degrading effects through the use of multiple energy ranges. The evaluation, using both a physical phantom experiment and an XCAT phantom simulation, demonstrated more accurate modeling of the image formation process and more accurate organ activity estimates than previous methods. </p><p> We then developed new methods for optimizing the acquisition energy window and parallel-hole collimator, respectively, for quantitative imaging. These methods account for the effects of energy window or collimator on both the bias and the variance of the activity estimates, and are applicable to radionuclides with any type of emission energy spectra. We applied these methods to optimizing the energy window and collimator for quantitative <sup>90</sup>Y bremsstrahlung SPECT in microsphere brachytherapy. </p><p> In addition to improving the reliability of quantitative imaging, we also did some work on improving the visual image quality for <sup>90</sup>Y bremsstrahlung SPECT imaging. We optimized the energy window for a detection task based on the performance of an observer that accounts for the degradation of the image quality due to model-mismatch. This is important as detection of post-administration extra-hepatic 90Y could be useful in predicting and preparing for complications such as radiation-induced gastro-intestinal ulcerations. </p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3572709 |
| Date | 02 October 2013 |
| Creators | Rong, Xing |
| Publisher | The Johns Hopkins University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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