A schematic diagram of 4D radiotherapy to account for intrafraction motion. The solid lines indicate the current information flow of the treatment plan to radiation delivery, and the dashed lines indicate the additional information feedback loop required for 4D radiotherapy. “4DC” is the four-dimensional controller that takes as input the treatment parameters, such as the multileaf collimator (MLC) planned positions and the tracking signal. The tracking signal can potentially be any signal, though in this case it is the implanted marker positions. The outputs of 4DC are the MLC leaf motion positions, which may require prediction depending on the time to complete the feedback loop.
A picture of the gold markers inserted into the “tumor” of the phantom.
The geometry (a) simulated and (b) used in this experiment.
(a) The phantom on the oscillating platform during treatment delivery with the electronic portal imaging device (EPID) in position and (b) a close-up view of the phantom, oscillating platform, and driving motor.
The acquisition settings used for (a) regular clinical image acquisition and (b) the fast image acquisition settings used. Note the difference in acquisition time from .
A flow diagram of the image-processing steps required to determine the marker positions, corresponding with box 3 in Fig. 7 for detecting marker centroids.
A flow diagram of the pretreatment and during-treatment steps for electronic portal imaging device (EPID)-based implanted marker tracking for 4D radiotherapy.
A comparison of the lung phantom images acquired using (a) regular clinical image acquisition settings and (b) fast image acquisition settings.
Images of the moving phantom acquired at minimum velocity (a) and maximum velocity [both (b) and (c)]. The top row shows the raw images, while the bottom row shows the images with the automatically determined positions marked. Although the image acquisition time was , both the markers and the outline of the tumor are blurred due to motion.
The automatically determined positions of the centroid of the three markers from the dynamic phantom images (diamonds) and the static phantom images (squares). The error bars are of an electronic portal imaging device (EPID) pixel .
The noise and signal-noise ratio for clinical (static phantom), fast settings (static phantom), and fast settings (phantom velocity ). The noise is defined as the standard deviation of the pixel-pixel variations in a uniform region. The signal-noise ratio is defined as the ratio of the difference between the maximum pixel value for the marker and the background divided by the noise.
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