TABLE 1.

Technical specifications of three representative CyberKnife® models.

	CyberKnife circa 1997–1999	CyberKnife VSI 2009	CyberKnife M6/S7 2012/2020
Robotic manipulator type and precision	FANUC robot 0.5 mm precision	KUKA KR 240 robot 0.12 mm precision	KUKA KR 300 R2500 ultra robot 0.12 mm precision
Beam collimation	Fixed circular collimators	Fixed circular collimators Iris variable aperture collimator	Fixed circular collimators Iris variable aperture collimator InCise Multileaf Collimator (2014)
Image registration and tracking methods	Skull skeletal tracking with 3D translation corrections	Skull skeletal tracking with 6D translation and rotation corrections Spine skeletal tracking with 6D corrections Fiducial marker tracking with 6D corrections Lung tumor tracking based on tumor: lung radiographic contrast with 3D corrections	Skull skeletal tracking with 6D translation and rotation corrections Spine skeletal tracking with 6D corrections Fiducial marker tracking with 6D corrections Lung tumor tracking based on tumor: lung radiographic contrast with 3D corrections
Real time respiratory motion tracking		Synchrony with fiducial and lung tumor tracking	Synchrony with fiducial, lung and spine prone tracking.
Overall targeting accuracy (static target)	Mean: 1.6 mm. Range: 0.6–2.5 mm 24 E2E in phantom	Spec: ≤0.95 mm E2E in phantom	Spec: ≤0.95 mm E2E in phantom
Overall targeting accuracy (target undergoing respiratory motion)	n/a	Spec: ≤1.5 mm (v9.6 and before) ≤0.95 mm (v10.0 and after) E2E in phantom	Spec: ≤1.5 mm (v9.6 and before) ≤0.95 mm (v10.0 and after) E2E in phantom
Dose rate	300 MU/min	600–1000 MU/min	1000 MU/min or 800 MU/min
Image detectors	Gadolinium oxysulfide fluoroscopes with pixel size 1.25 × 1.25 mm2	Amorphous silicon flat panel detectors with pixel size 0.4 × 0.4 mm 2	Amorphous silicon flat panel detectors with pixel size 0.4 × 0.4 mm 2
Dose calculation algorithm(s)	Ray Tracing	Monte‐Carlo Ray Tracing	Monte‐Carlo Ray Tracing FSPB
Patient positioning system	Manually operated treatment couch	Fully integrated 5‐DOF standard treatment couch with manual yaw adjustment Fully integrated 6‐DOF robotic couch Patient Positioning System (option) Fully integrated 7‐DOF robotic couch with seated load (option). The 7th DOF is knee up position option.	Fully integrated 5‐DOF standard treatment couch with manual yaw adjustment Fully integrated 6‐DOF robotic couch Patient Positioning System (option)
Clinical applications	Intracranial and upper spine radiosurgery (under FDA Investigational Device Exemption)	Anywhere in the body where radiosurgery is clinically indicated (with FDA 510(k) regulatory clearance).	Anywhere in the body where radiosurgery is clinically indicated (with FDA 510(k) regulatory clearance).

The targeting accuracy for the 1997–1999 model is reported by Murphy et al. in 1996. All other targeting accuracy information is from manufacturer's specification.