Performance evaluation of the CyberKnife system in real-time target tracking during beam delivery using a moving phantom coupled with two-dimensional detector array

  • Bin YangEmail author
  • Tin Lok Chiu
  • Wai Kong Law
  • Hui Geng
  • Wai Wang Lam
  • Tat Ming Leung
  • Lok Hang Yiu
  • Kin Yin Cheung
  • Siu Ki Yu


The aim of the current study was to evaluate the tracking error of the Synchrony Respiratory Tracking system by conducting beam-by-beam analyses to determine the variation in the tracking beams measured during target motion. A moving phantom of in-house design coupled with a two-dimensional (2D) detector array was used to simulate respiratory motion in the superoinferior (SI) and anteroposterior (AP) direction. A styrofoam block with four implanted fiducial markers was placed on top of the detector to enable the fiducial-based respiratory tracking. Measurements were performed with the phantom under either stationary mode or sinusoidal motion of 6-s cycle and 15/20-mm amplitude at SI and AP direction. The measurement data were saved as movie files that were used to calculate the center shift of the beam with 100-ms sampling time. The tracking accuracy of the system was defined as the targeting error, which could be tracked with probability of > 95% (Ep95). The mean ± standard deviation of Ep95 was 0.28 ± 0.08 mm under stationary condition; 0.66 ± 0.23 mm (range: 0.28–1.22 mm) under sinusoidal respiratory motion. The maximum drift of the beam center for all beam paths was 2.7 mm. The tracking accuracy of CyberKnife Synchrony system was successfully evaluated using a moving phantom and 2D detector array; the maximum tracking error was < 1.5 mm for sinusoidal motion of amplitude ≤ 20 mm.


CyberKnife Synchrony Target-tracking accuracy 2D detector array 


Compliance with ethical standards

Conflict of interest

The authors have no relevant conflicts of interest to disclose.

Statement of human and animal rights

This study included no animals or humans.

Informed consent

Informed consent was not necessary, because no human subjects were involved in this work.


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Copyright information

© Japanese Society of Radiological Technology and Japan Society of Medical Physics 2019

Authors and Affiliations

  1. 1.Medical Physics and Research DepartmentHong Kong Sanatorium & HospitalHong KongChina
  2. 2.Biomedical Engineering DepartmentHong Kong Sanatorium & HospitalHong KongChina

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