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Potential underestimation of the internal target volume (ITV) from free-breathing CBCT
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Image of FIG. 1.
FIG. 1.

Simulated respiratory profiles with five different inspiration to expiration ratios with a motion amplitude of 2 cm.

Image of FIG. 2.
FIG. 2.

Smoothed and normalized patient respiratory profiles with six varying inspiration to expiration ratios plotted as a function of 2 cm amplitude.

Image of FIG. 3.
FIG. 3.

FB-CBCT images of the five simulated respiratory profiles. The ratio of time spent in inspiration to expiration is indicated on the bottom right corner of each FB-CBCT.

Image of FIG. 4.
FIG. 4.

Demonstration of the calculation of percentage contrast reduction along the direction of motion of the ITV from the FB-CBCT image.

Image of FIG. 5.
FIG. 5.

FB and 4D phase images of two patient respiratory profiles (top row) and two simulated respiratory profiles (bottom row). The number indicated on FB image represents the inspiration to expiration ratio, whereas the percentage indicated on the adjacent images represents the phase bin. Peak inspiration corresponds to 0% and peak expiration corresponds to 50%.

Image of FIG. 6.
FIG. 6.

The local contrast computed along line profiles of the FB-CBCT images of the simulated respiratory cycles for both target sizes (T) and all three motion amplitudes (A). The legend on the right indicates the correlation between respiratory profile and marker shape.

Image of FIG. 7.
FIG. 7.

Local contrast plotted for patient respiratory profiles along the direction of motion in the FB-CBCT images for all target sizes (T) and motion amplitudes (A), in addition to the gold-standard profile, which has a perfect simulated inspiration to expiration ratio of one. The legend relates each respiratory profile with its corresponding marker shape.

Image of FIG. 8.
FIG. 8.

Area in pixels calculated using Canny edge detection for the 1.0 cm target for both simulated and patient respiratory profiles. The area is computed as a function of the standard deviation of the filter used by the image-processing technique.

Image of FIG. 9.
FIG. 9.

The results for the pixel area computed using Canny edge detection on the FB-CBCT images of the 3.0 cm target for all respiratory profiles (simulated and patient) for three sigma values. These sigma values represent the standard deviation of the filter used to determine the edges by the algorithm.

Image of FIG. 10.
FIG. 10.

Coronal slices of FB-CBCT and 4D CBCT phase images for the lung cancer patient tumors along with the corresponding RPM profile.


Generic image for table

Percentage of contrast reduction computed from FB-CBCT images of motion phantom for all cases. The first five rows of the table display the results for the simulated respiratory cycles and the last six rows depict the results for the patient respiratory cycles. T represents target size and A represents amplitude, both in centimeters so that T1A0.5 = 1.0 cm target and 0.5 cm amplitude, T3A2 = 3.0 cm target and 2.0 cm amplitude, etc.

Generic image for table

Percent underestimation of the 4D CBCT ITV by the FB-CBCT ITV for both patient lung tumors A and B.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Potential underestimation of the internal target volume (ITV) from free-breathing CBCT