Fig 1.
The cone beam computed tomography (CBCT) of a Gamma Knife Icon.
(a) The CBCT at its maximum rotation angle for imaging. (b) A CBCT geometrical accuracy verification phantom. There are four ball bearings with known positions. (c) The maximum deviations of the four ball bearings were measured throughout the year after installation.
Fig 2.
The white arrows show four of the fifteen arbitrary landmarks used for coordinate measurements in a reference CBCT image set of a CIRS radiosurgery head phantom.
Fig 3.
The procedure used to examine the accuracy of stereotactic coordinate assignment.
A fiducial marker-based system was defined using the fiducial markers in the stereotactic CT images. A co-registration-based system was assigned by co-registering the stereotactic CT images with reference CBCT images. A CBCT-based system was intrinsically defined so that its center was calibrated to the radiation focus. The coordinates of the landmarks measured in each coordinate system were compared.
Fig 4.
Region of co-registrations used in this study.
The dotted line corresponds to the ‘Low’ region, the solid line to the ‘Mid’ region, and the dashed line to the ‘High’ region. The ‘Large’ region is the total area of all three regions.
Fig 5.
One- and three-dimensional deviations measured based on co-registration between CBCT images.
(a), (b) before co-registration; (c), (d) after co-registration without any movement; (e), (f) with rotations only; and (g), (h) with arbitrary movements.
Fig 6.
The accuracies of co-registration between CBCT images.
Mean and standard deviations of the one- and three-dimensional deviations of the fifteen landmarks before and after the co-registration of CBCT images with reference CBCT images. BC: before co-registration; NM: no movement; RO: rotation only; and AM: arbitrary movement.
Fig 7.
One- and three-dimensional deviations measured based on the co-registration of CBCT images and stereotactic CT images.
(a), (b) before co-registration; (c), (d) after co-registration without any movement; and (e), (f) with arbitrary movements.
Fig 8.
The accuracies of co-registration between CBCT and CT images.
Means and standard deviations of the one- and three-dimensional deviations of the fifteen landmarks before and after co-registration between CBCT images and stereotactic CT images. BC: before co-registration; NM: no movement; and AM: arbitrary movement.
Fig 9.
The differences between fiducial marker-based and co-registered MR images.
(a), (b) One- and three-dimensional deviations of AC and PC. (c) Translation parameters reported by the co-registration program. (d) Mean three-dimensional deviations of AC and PC obtained after co-registration using four ROCs.
Table 1.
Means and standard deviations of the coordinate transformation parameters reported by LGP.
One- and three-dimensional deviations in the positions of the AC and PC are also shown. (angle unit: degree, length unit: mm).