Master of Science (MS)
Physics and Astronomy
Purpose: Compare the localization accuracy of 3D cone beam computed tomography (CBCT) and 4D CBCT for a dynamic respiratory phantom, considering cases with and without respiratory variations between planning and treatment. Methods and Materials: A respiratory phantom was imaged using 3D CBCT and 4D CBCT. Measurements of the amplitude of motion in 3D CBCT and 4D CBCT and size of the sphere at its exhale position in 4D CBCT were acquired. The phantom was then misaligned by known distances relative to a reference position. 3D CBCT and 4D CBCT were used to re-align the phantom by comparing localization images to reference images. Because the ideal 4D CBCT registration approach was to be determined, multiple localization-reference pairs of images were examined. Comparison was performed for multiple respiratory waveforms at two amplitudes as well as for waveforms where amplitudes were increased or decreased by 30%, simulating changes in respiratory behavior between simulation and localization. Error of localization trials was defined as the difference between the recommended table shifts and the known displacement. Results: Measurements of the respiratory amplitude were underestimated for all cases. Measurement of the sphere diameter exhibited < 2 mm error. Localization errors were less than 2.6 mm for all cases. When the motion amplitude was the same during localization as planning, automatic registration of the exhale frame from the 4D CBCT to the reference exhale frame had the smallest error in localization of 0.54 ± 0.03 mm. However, automatic registration of the 4D CBCT AIP to the reference AIP had the smallest errors when the motion amplitude changed between planning and localization, 1.59 ± 0.12 mm for the +30% amplitude change and 0.69 ± 0.02 mm for the -30% amplitude change. Conclusion: Because lung tumor motion amplitude throughout treatment may vary between planning and treatment, the use of 4D CBCT AIP registered to reference AIP was recommended for localization. 4D CBCT provided additional benefits compared to 3D CBCT of substantial reduction in target blurring and verification of respiratory motion characteristics prior to treatment.
Document Availability at the Time of Submission
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Woods, Runyon Colie, "Comparison of 3D and 4D CBCT for the Localization of Moving Targets" (2015). LSU Master's Theses. 1407.
Fontenot, Jonas David