A fast, accurate, and automatic 2D–3D image registration for image‐guided cranial radiosurgery

Abstract

The authors developed a fast and accurate two-dimensional (2D)-three-dimensional (3D) image registration method to perform precise initial patient setup and frequent detection and correction for patient movement during image-guided cranial radiosurgery treatment. In this method, an approximate geometric relationship is first established to decompose a 3D rigid transformation in the 3D patient coordinate into in-plane transformations and out-of-plane rotations in two orthogonal 2D projections. Digitally reconstructed radiographs are generated offline from a preoperative computed tomography volume prior to treatment and used as the reference for patient position. A multiphase framework is designed to register the digitally reconstructed radiographs with the x-ray images periodically acquired during patient setup and treatment. The registration in each projection is performed independently; the results in the two projections are then combined and converted to a 3D rigid transformation by 2D-3D geometric backprojection. The in-plane transformation and the out-of-plane rotation are estimated using different search methods, including multiresolution matching, steepest descent minimization, and one-dimensional search. Two similarity measures, optimized pattern intensity and sum of squared difference, are applied at different registration phases to optimize accuracy and computation speed. Various experiments on an anthropomorphic head-and-neck phantom showed that, using fiducial registration as a gold standard, the registration errors were 0.33 +/- 0.16 mm (s.d.) in overall translation and 0.29 degrees +/- 0.11 degrees (s.d.) in overall rotation. The total targeting errors were 0.34 +/- 0.16 mm (s.d.), 0.40 +/- 0.2 mm (s.d.), and 0.51 +/- 0.26 mm (s.d.) for the targets at the distances of 2, 6, and 10 cm from the rotation center, respectively. The computation time was less than 3 s on a computer with an Intel Pentium 3.0 GHz dual processor.

Development of an automatic evaluation method for patient positioning error

“…Yaw (rotation along the vertical axis) and pitch (rotation along the lateral axis) are the frontal image rotation and lateral image rotation, respectively. However, because roll (rotation along the longitudinal axis) cannot be determined from the frontal and lateral DRs, a 2D–3D registration method 4 , 5 , 6 , 7 , 8 , 9 , 10 is needed. In this evaluation of patient positioning error, it is assumed that the rotation error is negligible and can be almost ignored because the measurements take place after the patient positioning has been completed, and the pointing technique is also used for evaluation only regarding the translation errors.…”

“…For patient positioning research, CT–CT registration methods have been proposed using CT images or cone beam CT images, 1 , 2 , 3 2D–3D registration methods have been proposed using two‐directional X‐ray images, 4 , 5 , 6 , 7 , 8 , 9 , 10 and patient positioning systems that are fast and highly accurate are widely used. For patient positioning in particle therapy, the prescribed dose is not deposited to the target when the water‐equivalent path length (WEL) to the target changes, even if the target is positioned to the correct irradiation position using CT images 11 , 12 , 13 .…”

Evaluation of the accuracy and clinical practicality of a calculation system for patient positional displacement in carbon ion radiotherapy at five sites

“…The system for calculating patient positional displacement between DRs and DRRs was developed based on a 2D‐3D registration algorithm 14, 15, 16. The system can calculate the positional displacements between the DR and DRR.…”

Editorial: The biological advantage of single-session radiosurgery

“…This was not our motivation; numerous studies have confirmed the CyberKnife's ability to deliver highly focal doses of radiation with submillimeter accuracy. [1][2][3][4] Thus, "setup error" is not one of the contributing factors to the study's observed differences.…”