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Quantitative Assessment by Measurement and Modeling of Mobile Target Elongation in Cone-Beam Computer Tomographic Imaging

I Ali

I Ali*, N Alsbou, O Algan, T Herman, S Ahmad, Oklahoma Univ. Health Science Ctr., OKLAHOMA CITY, OK

WE-G-134-9 Wednesday 4:30PM - 6:00PM Room: 134

Purpose: To assess quantitatively elongation of mobile targets in cone-beam CT (CBCT) imaging by measurement and modeling. A mathematical model was derived that predicts the measured lengths of mobile targets and its dependence on target size and motion patterns in CBCT imaging.
Method and Materials: Three tissue-equivalent targets of differing sizes were inserted in an artificial thorax phantom to simulate lung lesions. Respiratory motion was mimicked with a mobile phantom that moves in one-dimension along the superior-inferior direction at a respiration frequency of 15 cycles per minute for eight different ranges of motion (0-40 mm). The phantom was imaged with CBCT using a kV on-board imager mounted on a TrueBeam Varian linear accelerator. The target lengths were measured on CBCT images with different motion patterns. A mathematical model was derived to quantify the variations in target lengths and its dependence on phantom motion parameters in CBCT. Predictions of the model were verified by comparison with measurement of the lengths of mobile targets in CBCT images.
Results: The model predicts that target lengths increased linearly with increase in speed and amplitude of phantom motion in CBCT. The measured lengths of mobile targets imaged with CBCT agreed with the calculated lengths within half-slice thickness spatial resolution. The maximal length of a mobile target was independent of the frequency and phase of motion. Elongation of mobile targets was similar in half-fan and full-fan CBCT for similar motion patterns as long as the targets remained within the imaging view.
Conclusion: Mobile targets elongated linearly with phantom speed and motion amplitude in CBCT imaging. The model introduced in this work assessed quantitatively the variation in target lengths induced by motion which may be a useful tool to consider elongations of mobile targets in CBCT applications in diagnostic imaging and radiotherapy.

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