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Liver motion during cone beam computed tomography guided stereotactic body radiation therapy
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Image of FIG. 1.
FIG. 1.

(a) The overall workflow of the marker extraction process. The extraction is performed simultaneously in the two opposing directions until either they meet at the last overlapping projection or the markers are absent in the image. (b) The height and width positions extracted as a function of the projection angle.

Image of FIG. 2.
FIG. 2.

Illustration of the process in which a 1D respiratory motion trajectory line is obtained. The projections are sorted into either a high-amplitude or low-amplitude signals. Then a line is drawn to intersect the two average points.

Image of FIG. 3.
FIG. 3.

An illustration of how a 3D marker position is estimated. An orthonormal point along the function f fid is calculated that lies closest to the f axial line.

Image of FIG. 4.
FIG. 4.

Comparison of simulated marker tracking results with the ground truth in the AP (a), LR (b), and CC (c) directions with constant breathing, and the AP (d), LR (e), and CC (f) directions with random breathing. Note that CC motion in both cases (c, f) appear to be a single line due to an almost exact overlap with each other.

Image of FIG. 5.
FIG. 5.

Trajectories of all 49 markers reconstructed, during their 1st fraction CBCT scans, viewed from the (a) anterior, (b) posterior, (c) left, and (d) right beam's eye view.

Image of FIG. 6.
FIG. 6.

An example patient showing the three types of LR motion with the corresponding three markers implanted.

Image of FIG. 7.
FIG. 7.

Four representative patients illustrating the typical interfractional and intrafractional motion variations: (a) Patient #1, (b) Patient #14, (c) Patient #18, and (d) Patient #12. Also shown is the “MIP margin” motion range determined by the planning MIP CT.

Image of FIG. 8.
FIG. 8.

The appropriate % gating window determined based on the marker motion trajectory of each fraction, for each patient.

Image of FIG. 9.
FIG. 9.

The intermarker motion variability in the (a) LR, (b) AP, and (c) CC directions, for Patient #20.

Image of FIG. 10.
FIG. 10.

Scatter plot showing the absolute intermarker motion magnitude difference as a function of the marker-to-marker separation.

Image of FIG. 11.
FIG. 11.

Typical projection images taken with the (a) pelvis mode, and the (b) low-dose thorax mode. The white dotted circles indicate where the markers should be located.


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Patient characteristics data. S1–S8 represent the standard liver anatomy segments.

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Three types of motion relationships identified along the LR and the AP/CC directions, that is, when the marker moves toward the cranial-posterior direction, it also moves to the: (Type I) patient-right, (Type II) patient-left, and (Type III) minimal/none motion.

Generic image for table

The comprehensive list of peak-to-peak amplitude, across the three dimensions, and the breathing period observed during the 4DCT simulation and the CBCT scans. The two cases with the most significant intermarker motion variations are underlined.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Liver motion during cone beam computed tomography guided stereotactic body radiation therapy