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Quantitative Measurement and Modeling of Target Volume Changes by Respiratory Motion in CT and Cone-Beam CT

S Jackson

S Jackson*, S Ahmad, I Ali, Oklahoma Univ. Health Science Ctr., Oklahoma City, OK

SU-E-J-133 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Variations in the target volume and length in CT and cone-beam CT (CBCT) imaging by respiratory motion were investigated for different motion amplitude and frequency. A model that predicts the target volume dependence on motion amplitude, frequency, target size, speed of CT and CBCT scanning was developed.
Method and Materials: Three target volumes of differing sizes were constructed of tissue-equivalent gel material and embedded into artificial lung phantom. Respiratory motion was mimicked by a mobile phantom at a respiration frequency of 15 cycles/min for eight different amplitudes of respiratory motion in the range 0-20 mm. Images obtained for CT and CBCT were contoured and the target volumes and superior-inferior lengths were calculated. A mathematical model was developed to quantify and reproduce observed variations in target volumes and lengths due to motion artifacts.
Results: The measured volumes and lengths of the different targets increased by blurring artifacts of respiratory motion in CBCT images because of long scanning times (about 1 minute), which was found to enlarge linearly with the respiratory motion amplitude. However, in CT, the target volumes and lengths could increase or decrease by imaging depending on whether the CT scanning was parallel or opposed to the moving phantom. The mathematical model predicts very well the variation in target volumes imaged by CT and CBCT as a function of motion amplitude, frequency, target size, speed of CT and CBCT scanning
Conclusion: The measurement and modeling of target volume and length variations provided quantitative assessment of induced artifacts in CBCT and CT imaging by respiratory motion. The modeling of imaging artifacts induced by respiratory motion in CT and CBCT can be used to define accurately gross tumor volumes and organs-at-risk which will be very useful for accurate treatment planning, target localization, motion tracking and beam gating during dose delivery.

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