CyberKnife robotic radiosurgery

CyberKnife, invented by Stanford neurosurgeon John Adler and first used in 1994, mounts a compact 6 MV linac on a six-axis robot. Instead of a gantry rotating about one isocentre, the robot visits many nodes around the patient and delivers non-isocentric, non-coplanar beams shaped by fixed cones or a variable-aperture or multileaf collimator. Two ceiling-mounted kilovoltage X-ray cameras image the skull, spine or implanted fiducials throughout treatment and the robot corrects its aim, and the Synchrony system models the breathing cycle from chest markers so the beam moves with a lung, liver or pancreatic tumour rather than treating a widened margin. That made frameless brain radiosurgery, spinal radiosurgery and five-fraction prostate SBRT practical and it treats trigeminal neuralgia and benign tumours as well.

Compared with a modern C-arm linac fitted for stereotactic work, CyberKnife tracks motion natively and reaches unusual beam angles, but sessions are long (often thirty to sixty minutes or more), fields are small so it does not treat large or conventional volumes, and throughput is low, which keeps it in dedicated stereotactic programmes. Gamma Knife remains the comparator for intracranial targets and linac-based SRS is the mass-market alternative.