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Evaluation of the Rotational Alignment Accuracy and Error Using 3D/3D, 2D/3D and 3D Surface Registration

H Kuo*, A Ballangrud , G Li , D Lovelock , B Wolthuis , C Della-Biancia , S Berry , M Hunt , Memorial Sloan Kettering Cancer Center, New York, NY


(Tuesday, 7/16/2019) 9:00 AM - 10:00 AM

Room: Pins Room | Hall 2

Purpose: To intercompare two 3D/3D registration platforms, one 2D/3D registration method, and one 3D surface registration method. These three technologies are available to perform 6D registrations for image-guided radiotherapy treatment.

Methods: Twelve and eight fiducial markers were asymmetrically placed on the surface of a head phantom and a body phantom, respectively. The solution of the rotational transformation between the two image sets (planning CT and CBCT) was optimized through least-squares fitting of the fiducial positions using singular value decomposition (SVD). This was used as the gold standard to evaluate the rotational accuracy of 3D/3D registration in Varian’s platform (3D3D_V), 3D/3D and 2D/3D registration in the BrainLab ExacTrac system (3D3D_E and 2D3D), as well as 3D surface registration in the AlignRT system (3DS). The phantoms were setup on a baseplate with random rotations in three axes (Rotation, Roll, and Pitch) within three degrees. 24 measurements (16 in head phantom, 8 in body phantom) of rotational shifts were made at five different intracranial isocenters using the SVD, the 3D/3D, 2D/3D, and 3D surface registration methods. Wilcoxon signed-rank test was utilized to compare the difference of each registration method with SVD. A p-value<0.05 was considered significant.

Results: Using SVD method as standard, all methods were significantly different at the Roll direction; 2D3D & 3DS were significantly different at Rotation direction; 3DS was significantly different at Pitch direction. Among the three axes, Roll direction was less well determined by all methods. Considering all rotational axis directions together, 3D3D_E and 3DS were significantly different. In terms of absolute rotational error at three directions (Rotation, Roll, Pitch), the mean±SD values for 3D3D_V, 3D3D_E, 2D3D, and 3DS were (0.1°±0.1°,0.2°±0.2°,0.1°±0.1°), (0.1°±0.1°,0.3°±0.2°,0.2°±0.1°), (0.3°±0.1°,0.6°±0.2°,0.2°±0.1°), and (0.3°±0.1°,0.3°±0.3°,0.4°±0.3°), respectively.

Conclusion: A truly 3D3D registration showed insignificant rotational alignment error. Partial 3D registration may double the error. All methods are clinically acceptable.


Cone-beam CT, Image-guided Therapy, Surface Matching


IM/TH- Image registration : Multi-modality registration

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