Quality assurance for an image-guided frameless radiosurgery system using radiochromic film.

Abstract

PURPOSE: The CyberKnife, a new type of machine for stereotactic irradiation, is composed of a combination of a robot (manipulator) and a linear accelerator; We measured the total pointing error of the therapy beam, aiming at improvement in the accuracy of the CyberKnife. METHODS AND MATERIALS: The CyberKnife keeps a number of coordinate systems such as the patient's coordinates, robotic coordinates, and IPS (image processing system) coordinates. Precise irradiation is possible if these coordinate systems are matched accurately. We always calculate the overall irradiation error using GAF MD-55 radiochromic film before irradiation treatment of the patient, and we have attempted to improve the accuracy of irradiation with the CyberKnife by feeding back the errors. RESULTS: The median of the error immediately after introducing the CyberKnife was 1.2 mm, and as a result of correction, we succeeded in reducing the error to 0.7 mm (median). Total pointing error after correction was significantly lower than that before correction (p=0.0023). CONCLUSIONS: This approach allowed us to reduce errors and establish a method for providing patients with highly accurate stereotactic irradiation. We believe these results endorse the validity of the method presented in this paper.