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Validation of Simulated Target Motion Spatial Accuracy of Elekta Symmetry Versus 4D CT

C Baley*, S Stathakis , P Myers , N Kirby , K Rasmussen , N Papanikolaou , D Saenz , University of Texas HSC SA, San Antonio, TX


(Sunday, 7/14/2019) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 5

Purpose: Elekta’s Symmetry software provides the capability to acquire 4D image acquisitions using cone-beam computed tomography (CBCT). The development of 4D CBCT provides more precise tracking of mobile tumors. The aim of this study was to validate Symmetry’s accuracy when compared to an established 4D computed tomography (CT) technique.

Methods: A 4D CBCT was obtained of the CIRS motion phantom using Symmetry and compared to a 4D CT of the same phantom using C-RAD Sentinel surface imaging. The phantom included inferior/superior motion with an amplitude of 15 mm and 4 s cycle. Similarly, surrogate motion had an amplitude of 15 mm and 4 s cycle. The phantom’s motion variables were held constant between each imaging modality. The collected data was analyzed by automatic segmentation of the target in each phase of the 4D data sets. The target centroid of each phase was used to determine target trajectory. Target trajectories were fitted to a sinusoidal function, and the parameters of the fit were compared to determine agreement between each imaging modality.

Results: The sinusoidal curve fitted functions demonstrated submillimeter accuracy with amplitudes of 14.24 and 14.41 mm for 4D CT and 4D CBCT respectively. The correlation coefficient between the 4D CT and 4D CBCT target trajectories was 0.9887.

Conclusion: Elekta’s Symmetry application for 4D CBCT provided an accurate assessment of target location in the CIRS motion phantom when compared with 4D CT as the standard. Agreement between the two imaging modalities illustrates Symmetry’s ability to reproduce motion from the time of simulation and reduce uncertainty in tumor motion allowing for potential reductions in treatment planning margins.


Cone-beam CT, Lung, Image Guidance


IM/TH- RT X-ray Imaging: 4D CBCT imaging/therapy implementation

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