Abstract
Introduction: The CyberKnife (Accuray, Inc., Sunnyvale, California, USA) is an image-guided radiosurgical system which utilizes a compact 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgery. The total system error of the CyberKnife system, as measured with an anthropomorphic head phantom containing a film holder, has been previously reported to be submillimetric. In making these prior accuracy measurements, the Ball-Cube-I was used. However, a new design, the Ball-Cube-II, which uses a different kind of pre-cut films, has recently become available. In this study, we investigate the use of this device for measuring the total system accuracy of the CyberKnife. Methods: The Ball-Cube-II film cassette is a radiosurgical quality assurance (QA) tool. Similar to the existing Ball-Cube-I design, the Ball-Cube-II holds two pieces of notched radiochromic (www.gafchromic.com) film that are placed orthogonally within the film cassette. There are holes and pins in the film Ball-Cube-II cassette and holes in the EBT2 film, allowing the film to fit tightly, thus minimizing movement of the film with respect to the film cassette. The ball cube is then placed within an anthropomorphic phantom. The method for determining the localization accuracy of the CyberKnife System is similar for both film cube designs. More specifically, the spatial coordinates for the centroid of the planned dose distribution is compared with the centroid of the dose actually delivered. Results: Using the Ball-Cube-I with MD-55 film, and the head phantom, the total accuracy measured was 0.34 +/- 0.17 mm. While using the ball-cube II with EBT2 film, the total accuracy measured was 0.45 +/- 0.09 mm. Conclusions: The ball-cube-II restricts movement of the film inside the film cube, and thereby reduces the uncertainty of film placement within the cube. This design has the potential to more precisely determine the accuracy of the CyberKnife system. The accuracy of the CyberKnife using film cube with the head phantom was measured to be between 0.34 and 0.45 mm.
Highlights
The CyberKnife (Accuray, Inc., Sunnyvale, California, USA) is an image-guided radiosurgical system which utilizes a compact 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgery
The ball-cube-II restricts movement of the film inside the film cube, and thereby reduces the uncertainty of film placement within the cube. This design has the potential to more precisely determine the accuracy of the CyberKnife system
It uses a compact 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgical doses with submillimeter accuracy [2]
Summary
The CyberKnife (Accuray, Inc., Sunnyvale, California, USA) is an image-guided radiosurgical system which utilizes a compact 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgery. The total system error of the CyberKnife system, as measured with an anthropomorphic head phantom containing a film holder, has been previously reported to be submillimetric. In making these prior accuracy measurements, the Ball-Cube-I was used. It uses a compact 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgical doses with submillimeter accuracy [2]. Changes in patient position are detected by image-guidance using a pair of x-ray cameras (amorphous silicon detectors) and x-ray sources. The x-ray attenuation of the phantom and the radiographic appearance of the phantom in CT and x-ray images seek to emulate the human anatomy
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