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Positional accuracy of novel x-ray-image-based dynamic tumor-tracking irradiation using a gimbaled MV x-ray head of a Vero4DRT (MHI-TM2000)
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10.1118/1.4754592
/content/aapm/journal/medphys/39/10/10.1118/1.4754592
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/39/10/10.1118/1.4754592

Figures

Image of FIG. 1.
FIG. 1.

Photograph of an x-ray image-based dynamic tumor-tracking irradiation system. The system comprised a 3D moving phantom with a steel ball target, a laser displacement gauge, an orthogonal kV x-ray imaging subsystem, consisting of two sets of x-ray tubes and flat-panel detectors, a gimbaled MV x-ray head, and the system controller of the Vero4DRT. The gimbaled MV x-ray head enables rotation along the pan and tilt directions to track target motion, indicated by the imaging subsystem, while the laser displacement gauge synchronously measured the target motion in real time.

Image of FIG. 2.
FIG. 2.

Schematic diagram showing (a) data flow to demonstrate the x-ray image-based dynamic tumor-tracking irradiation system and (b) geometric point of the tracked target position, indicated by the gimbaled MV x-ray head with a tilt rotation angle of θ°. The predicted, measured, and tracked positions of the target were recorded in the system controller. The tracked target position was calculated from the rotation angle of the gimbaled MV x-ray head. The difference between the target positions predicted by the sequential prediction model and those measured by the laser displacement gauge was computed as prediction error (EP), and the difference between the target positions tracked by the gimbaled MV x-ray head and predicted target position was computed as mechanical error (EM). Total tracking system error (ET) was derived from EM and EP, computed as the difference between the target positions tracked by the gimbaled MV x-ray head and those measured by the laser displacement gauge.

Image of FIG. 3.
FIG. 3.

Variations in the measured and tracked positions of the target for sinusoidal patterns with (a) [peak-to-peak amplitude (A), breathing period (T)] = (40 mm, 2 s) and (b) (A, T) = (20 mm, 4 s), and circular patterns with (c) (A, T) = (40 mm, 2 s) and (d) (A, T) = (20 mm, 5 s). Solid lines show the measured positions of the target indicated by the laser displacement gauge, dashed lines show the tracked positions of the target indicated by the gimbaled MV x-ray head, and dotted lines show total tracking system errors (ET), expressed as the differences between the tracked and measured positions of the target.

Image of FIG. 4.
FIG. 4.

Variations in the measured and tracked positions of the target for (a) regular and (b) irregular respiratory cases. Solid lines indicate the measured positions of the target indicated by the laser displacement gauge, dashed lines show the tracked positions of the target indicated by the gimbaled MV x-ray head, and dotted lines show total tracking system errors (ET). Probability histograms as a function of the alignment error between the target and gimbaled MV x-ray head with or without tracking are shown for (c) regular and (d) irregular respiratory cases, respectively. Solid lines show the alignment error with tracking, and dashed lines show the alignment error without tracking.

Image of FIG. 5.
FIG. 5.

Variations in the tracking efficiency, defined as the ratio of twice the root mean square of ET (RMSET) to the peak-to-peak amplitude (A), as a function of principal component scores of patient respiratory motion. A strong positive correlation was observed between tracking efficiency and the principal component score (R = 0.91; p < 0.01).

Image of FIG. 6.
FIG. 6.

Schematic diagram of the simulation and variations of the simulated dosimetric error of mean dose in planning target volume (PTV) under the conditions of the displacements along the beam axis. The PTVs of 30 mm in diameter located at the displacements of −5, 0, and 5 mm from the isocenter with source-to-isocenter distance of 1000 mm were simulated under the condition of the one uniform field port adding 5-mm MLC margin. Dose calculation was performed under the same monitor unit with variance of 1% and a grid size of 2.3 × 2.3 × 2.5 mm3 using x-ray voxel Monte Carlo of well-commissioned 6 MV photon beam on a radiation treatment planning system (iPlan; BrainLAB, Germany).

Tables

Generic image for table
TABLE I.

Characteristics of the motion patterns.

Generic image for table
TABLE II.

Root mean squares of the EP, EM, and ET for sinusoidal and circular patterns.

Generic image for table
TABLE III.

Motion characteristics and root mean squares of the EP, EM, and ET for respiratory patterns.

Generic image for table
TABLE IV.

Principal component analysis for peak-to-peak amplitudes, breathing periods, and autocorrelation coefficients with a lag of one breathing period for 15 respiratory patterns.

Generic image for table
TABLE V.

Comparison of the characteristics of dynamic tumor-tracking (DTT) irradiation techniques.

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/content/aapm/journal/medphys/39/10/10.1118/1.4754592
2012-09-27
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Positional accuracy of novel x-ray-image-based dynamic tumor-tracking irradiation using a gimbaled MV x-ray head of a Vero4DRT (MHI-TM2000)
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/39/10/10.1118/1.4754592
10.1118/1.4754592
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