Flowchart of the proposed framework for tracking markers in low contrast MV images.
(a) The input MV image. (b) Histogram of gray levels in the input MV image on the left.
(a) The partial histogram of Fig. 2(b) . We use the minimum pixel value as the initial position of the kernel, denoted by the leftmost dot. The sequence of kernel locations converges at the local maximum, which corresponds to the foreground region in Fig. 2(a) . (b) Transformation function obtained using the iterative procedure in (a).
(a) Enhanced image using the proposed method. Arrows highlight the implanted markers. (b) Histogram of the enhanced image.
Comparison of local entropies obtained from the original images and the contrast-enhanced images of patient 1 (a) and patient 2 (b). The block size represents the length of one side of a square region centered on a fiducial marker.
(a) MV image of a patient with implanted cylindrical fiducial markers. Expected position of a selected marker is highlighted. (b) We search for marker candidates in a 41 × 41 search region (dotted box). The maker candidates found in the search region are highlighted by black color. (c) Detected marker position is highlighted. (d), (e), (f) are magnified images of (a), (b), (c), respectively.
Sequence of MV treatment beam imaging. The frames 1, 7, 8, 15, 16, 23, 24, and 25 are shown. These frames are selected to show how the treatment field changed in this MV sequence.
The number of mean shift iterations for the MV sequence shown in Fig. 7 .
Manually localized and automatically tracked marker positions for the MV sequence shown in Fig. 7 .
The timing diagram of our system (four markers).
Selected frames from a sequence of MV treatment beam images. These frames are selected to show how the MLC blocked region is changed during treatment. (Left column) Contrast-enhanced MV images and (right column) field mask.
Detection rates for the patients studied.
Comparison of tracking error and manual localization error.
Treatment gantry angles for the patients studied.
Comparison of tracking errors and manual localization errors at different gantry angles.
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