A New Method and Device for Calibration of High Definition Motion Management System of Gamma Knife ICON

Abstract

A motion tracking system which monitors patient motion and controls radiation delivery during Gamma Knife radiosurgical treatment is available with the Leksell Gamma Knife ICON machine. Yet the vendor provides no method or tool to calibrate the motion tracking system for commissioning and quality assurance programs. An easy-to-use method and tool is desired to confirm the spatial accuracy and precision of the motion tracking system. To that end, we have developed a new method and device and tested in our center. We developed a system of calibration and QA checks for the ICON high definition motion management (HDMM, also known as intra-fraction motion management) system, which consists of one 3D motion stage set, three stepper motor controllers, three stepper motorized actuators and a set of control software as shown in Figure 1. Measurements for tracking accuracy of the ICON HDMM system were conducted with the motion stage in left-right (X), anterior-posterior (Y) and superior-inferior (Z) directions separately. The HDMM system tracks the position of an infrared marker as a radial distance from a set origin. The motion stage was moved in well-defined displacements DX, DY and DZ for which the radial distance r = (DX2 + DY2 + DZ2)½ was calculated and compared to the HDMM system. The experimental tests were repeated and statistic analysis of the collected data was performed. Figure 1 Motorized QA system. The new motion stage system meets the specified accuracy (50mm/revolution). The mean value of r measured by HDMM was 0.19 mm with maximum standard deviation of 0.06 mm. The new QA system is easy-to-build and easy-to-use. The measurement is repeatable with high accuracy and precision. The ICON HDMM system can track patient motion with accuracy of less than 0.2 mm and precision of 0.06 mm.