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dc.contributor.advisor Yin, Fang-Fang en_US
dc.contributor.advisor Bowsher, James E en_US
dc.contributor.author Roper, Justin R en_US
dc.date.accessioned 2011-01-05T14:40:09Z
dc.date.available 2011-01-05T14:40:09Z
dc.date.issued 2010 en_US
dc.identifier.uri http://hdl.handle.net/10161/2986
dc.description Dissertation en_US
dc.description.abstract <p>On-board imaging is useful for guiding radiation to patients in the treatment position; however, current treatment-room imaging modalities are not sensitive to physiology - features that may differentiate tumor from nearby tissue or identify biological targets, e.g., hypoxia, high tumor burden, or increased proliferation. Single photon emission computed tomography (SPECT) is sensitive to physiology. We propose on-board SPECT for biological target localization.</p><p>Localization performance was studied in computer-simulated and scanner-acquired parallel-hole SPECT images. Numerical observers were forced to localize hot targets in limited search volumes that account for uncertainties common to radiation therapy delivery. Localization performance was studied for spherical targets of various diameters, activity ratios, and anatomical locations. Also investigated were the effects of detector response function compensation (DRC) and observer normalization on target localization. Localization performance was optimized as a function of iteration number and degree of post-reconstruction smoothing. Localization error patterns were analyzed for directional dependencies and were related to the detector trajectory. Localization performance and the effect of the detector trajectory were investigated in a hardware study using a whole-body phantom.</p><p>Typically targets of 6:1 activity were localized as accurately using 4-minute scans as those of 3:1 activity using 20-minute scans. This trend is consistent with the relationship between contrast and noise in the contrast-to-noise ratio (CNR) and implies that higher contrast targets are better candidates for on-board SPECT because of time constraints in the treatment room. Using 4-minute scans, mean localization errors were within 2 mm for superficial targets of 6:1 activity that were proximal to the detector trajectory and of at least 14 mm in diameter. Localization was significantly better (p < 0.05, Wilcoxon signed-rank test) with than without observer normalization and DRC at 5 of 6 superficial tumor sites. Observer normalization improved localization substantially for a target proximal to the much hotter heart. Localization error patterns were shown to be anisotropic and dependent on target position relative to the detector trajectory. Detector views of close approach and of minimal attenuation were predictive of directions with the smallest (magnitude) localization bias and precision. The detector trajectory had a substantial effect on localization performance. In scanner-acquired SPECT images, mean localization errors of a 22-mm-diameter superficial target were 0.8, 1.5, and 6.9 mm respectively using proximal 180°, 360°, and distal 180° detector trajectories, thus demonstrating the benefits of using a proximal 180° detector trajectory.</p><p>In conclusion, the potential performance characteristics of on-board SPECT were investigated using computer-simulation and real-detector studies. Mean localization errors < 2 mm were obtained for proximal, superficial targets with diameters >14 mm and of 6:1 activity relative to background using scan times of approximately 5 minutes. The observed direction-dependent localization errors are related to the detector trajectory and have important implications for radiation therapy. This works shows that parallel-hole SPECT could be useful for localizing certain biological targets.</p> en_US
dc.subject Engineering, Biomedical en_US
dc.subject Health Sciences, Oncology en_US
dc.subject Health Sciences, Radiology en_US
dc.subject biological imaging en_US
dc.subject radiation therapy en_US
dc.subject SPECT en_US
dc.subject target localization en_US
dc.title On-board Single Photon Emission Computed Tomography (SPECT) for Biological Target Localization en_US
dc.type Dissertation en_US
dc.department Medical Physics en_US

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