CyberKnife (Robotic Radiosurgery)
Robot-mounted 6 MV compact linear accelerator on a 6-axis industrial robotic arm. Treats targets throughout the body (not just intracranial like Gamma Knife) with real-time image-guided tracking.
What makes CyberKnife architecturally unique
- Robotic arm — the 6-axis industrial robot (adapted from KUKA automotive manufacturing arms) can position the linac at hundreds of non-coplanar beam angles. Conventional linacs rotate around a fixed isocenter in a single plane; CyberKnife doesn't have a fixed isocenter.
- Real-time tracking — orthogonal kV X-ray imaging during treatment tracks the target. Synchrony system compensates for respiratory and patient motion in real time. Other platforms require gating or breath-hold.
- No rigid frame — stereotactic precision without a skull frame. The tracking system replaces the immobilization.
- No gantry rotation — beams come from many directions but not via a rotating gantry.
Clinical applications
- Prostate SBRT — the dominant CyberKnife clinical indication. Fiducials implanted + tracked during delivery. Very short overall treatment course (5 fractions typical) vs conventional 40-fraction IMRT.
- Lung SBRT — moving target advantage.
- Spine SBRT — complex dose geometry around cord.
- Brain SRS — cranial radiosurgery alternative to Gamma Knife.
- Liver / pancreas SBRT — moving-target advantage.
- Reirradiation — when prior RT limits options and precision matters.
Key specs
- Linac energy — 6 MV photons only (no electrons, no dual-energy)
- Dose rate — 1000 MU/min (recent generations)
- Collimation — InCise 2 MLC (current) + fixed cones + Iris variable collimator (legacy)
- Imaging — kV-kV orthogonal (2 ceiling-mounted kV tubes + 2 floor amorphous-silicon detectors)
- Motion management — Synchrony (real-time tracking)
Systems
- CyberKnife S7 (current)
- CyberKnife M6 (widely deployed predecessor)
- CyberKnife VSI (legacy)
Competitive positioning
vs Varian Edge:
- Edge: faster per fraction (higher dose rate), conventional gantry geometry, broad linac capability (can do IMRT/VMAT as well)
- CyberKnife: more non-coplanar angles, better real-time tracking, dedicated SRS/SBRT (no volume IMRT workload)
- Unity: real-time MRI visualization (soft tissue)
- CyberKnife: real-time X-ray tracking (of fiducials or bony anatomy)
vs Gamma Knife (intracranial only):
- Gamma Knife: 192 cobalt sources, sub-mm mechanical precision, sharper dose falloff on small intracranial targets
- CyberKnife: intracranial + extracranial, robotic flexibility, linac-based physics
Regulatory
- State radiation facility license
- No NRC (uses X-rays, not radioactive sources — unlike Gamma Knife)
- QMP + RSO
- TG-142 adapted for CyberKnife's non-standard geometry