A fiducial marker system using digital techniques

A FIDUCIAL MARKER SYSTEM USING DIGITAL TECHNIQUES SOFTWARE

As can be seen in Figure 4.3, the tracked motion agrees with the known sinusoidal movement of the fiducial embedded in the pelvic phantom to within 1 mm. Figures 4.2 and 4.3 demonstrate the technique using a moving pelvic phantom. 9, 10 The maximal frames per second (fps) obtainable from the kV and MV detectors in VarianвЂ™s Trilogy (Varian Medical Systems, Palo Alto, Calif), for example, are 15 Hz and 9 Hz, respectively. 4.1) is possible during either fixed gantry or arc therapy. However, localization of implanted markers with hybrid use of onboard kV and treatment MV beams ( Fig. Disadvantages of the onboard fluoroscopic systems include the inability to acquire both images simultaneously, making real-time positioning (e.g., for respiratory motion management) challenging. Additional advantages of using these systems for fiducial localization are that the image orientation can be selected for optimal marker visualization and separation of the two image sets required for three-dimensional (3D) marker localization can be performed. The spatial accuracy of coordinate mapping from these images to isocenter is excellent. 8 The systems are used to image the patient for positioning purposes, which includes imaging of fiducial markers. The systems consist of x-ray tubes and solid-state imaging panels placed on opposite sides of the linear accelerator isocenter. These systems typically operate at 120 to 140 kVp. Modern linear accelerators are often provided with onboard coregistered kV imaging systems. Images can also be acquired using onboard kV systems. For example, surgical clips often provide insufficient image contrast to allow them to be localized in the image. Because of the penetration of MV photons to metals, the relatively high scatter-to-primary ratio, and the lack of scatter rejection hardware in portal imagers and MV film cassettes, marker design is critical to visualization and detection with MV imaging. If the patient is repositioned, the user generally has the option of reacquiring the images after repositioning to verify that the shift was conducted correctly. This position is compared against the planned position, and the difference is presented to the user so he or she can determine whether the patient needs to be repositioned.

A FIDUCIAL MARKER SYSTEM USING DIGITAL TECHNIQUES SOFTWARE

Typically, commercial software is used that provides the user with tools to identify the markers on the image, which the software uses to establish the location of the markers in the treatment room coordinate system. At least two images are acquired with sufficiently large angular separation to allow the measurement of all three spatial coordinates of the marker. Typically, the radiation beam is operated at a relatively low dose (1 to 3 cGy) that is sufficient to expose the film or imager. 1, 2, 3, 4, 5, 6, 7 The portal films or images are typically acquired to localize the patient position either before or during the radiation treatment and to use the treatment beam and a portal imager.

The most common process for accomplishing this is through the acquisition of MV portal films or images. The image-based method for fiducial marker localization requires acquisition of two or more radiographic images.

A fiducial marker system using digital techniques