TH-AB-303-07: Evaluation of Tumor Tracking Accuracy of CyberKnife Synchrony System Using a Plastic Scintillator

Abstract

Purpose: For CyberKnife Synchrony System, the tracking accuracy is critical for achieving desired dose delivery. In this study, we evaluated the tracking accuracy using a real-time image acquisition of the scintillation light produced by a plastic scintillator plate. Methods: A CyberKnife G4 system was used. A graph paper with 8 × 13 cm rectangular hole was attached on a U-shaped plastic plate. Pieces of fluorescent tape and three metallic markers were also attached on the plate. The plastic plate was moved with a 3D motion phantom as slipping on a 30 cm × 30 cm × 1 cm of plastic scintillator plate. Tumor motions derived from orthogonal cine-MRI images were used for phantom motion. The plastic scintillator was irradiated in a dark treatment room using the Synchrony System for tracking the metallic markers. During irradiation, the light of the scintillator and fluorescent tape were recorded as a video using a CMOS sensor camera. The centroid of the scintillation and fluorescent light were analyzed using an in-house software after image processing including geometric calibration, noise reduction, and extraction of blue color channel. Results: The intensity of the scintillation light was sufficient for identification of the irradiated position. The acquired data showed respiratory signal similar to the data transferred to the phantom, although positional variation due to machine head motion was observed. The difference of the position between the scintillation light and phantom motion was −0.07 mm ±0.76 mm. The 10%, 50%, 75%, and 90% percentile of the difference was −1.04 mm, −0.59 mm, −0.09 mm, 0.44 mm, and 0.91 mm, respectively. The correlation coefficient R2 between these two positions were 0.992. Conclusion: We developed a verification system of the CyberKnife Synchrony System which visualizes the tracking accuracy using a plastic scintillator. This work was supported by JSPS KAKENHI Grant Number 26860402 and 24791300.