Gamma Knife vs CyberKnife: Platforms, Frame vs Frameless, and What Actually Differs

Gamma Knife and CyberKnife are both stereotactic radiosurgery platforms, but they differ in the radiation they use and what they can reach: Gamma Knife delivers cobalt-60 gamma rays from a fixed source array to intracranial targets only, while CyberKnife delivers 6 MV X-ray photons from a linear accelerator on a robotic arm and can also treat the body and spine. For a small, well-defined brain target the radiation effect on tissue is broadly comparable, so the choice usually comes down to the target, its location and what a given centre owns¹.

When I was weighing up treatment for my acoustic neuroma, the two names came up in the same breath, as if I had to pick a favourite brand. I did not, and the distinction that actually mattered turned out to be narrower and more mundane than the marketing around each machine suggests. This is the plain comparison I wish I had been handed. For the full picture of the treatment itself, start with Gamma Knife radiosurgery, and if you want the underlying category, read what is stereotactic radiosurgery.

What is the difference between Gamma Knife and CyberKnife?

The core difference is the radiation source and the range of the machine: Gamma Knife uses gamma rays from fixed cobalt-60 sources and treats the brain only, whereas CyberKnife uses X-ray photons from a linear accelerator mounted on a robotic arm and can treat the brain, the body and the spine. Both are forms of stereotactic radiosurgery, meaning they focus many beams of radiation so they converge on a target and deliver a high dose there while sparing the tissue around it. The names sound like rival products, but they describe two engineering routes to the same idea¹.

Gamma Knife is made by Elekta as the Leksell Gamma Knife, and its beams converge to an accuracy of under about 0.5 mm². CyberKnife achieves comparable precision differently, by moving its arm and re-imaging as it goes. Neither is universally superior; they are suited to different jobs. For how the beams add up in the Gamma Knife itself, see how Gamma Knife works.

How do the radiation sources compare: cobalt-60 vs LINAC photons?

Gamma Knife uses gamma rays emitted by decaying cobalt-60 sources; CyberKnife uses X-ray photons produced by a linear accelerator at 6 MV. Current Gamma Knife units use 192 cobalt-60 beams (older units used 201), aimed so they cross at the target. CyberKnife instead generates its radiation on demand in a compact linear accelerator, then points that single beam from many angles using the robotic arm¹.

The distinction is in how the radiation is made, not in how much of it reaches the target. Gamma rays and 6 MV X-ray photons deposit their energy in tissue in broadly comparable ways, which is why the biological effect on a given target is similar. What differs is the delivery: a fixed array of sources for Gamma Knife, a moving beam for CyberKnife. One practical footnote is that cobalt-60 sources decay over years and are periodically replaced, whereas a linear accelerator is switched on and off; that is a service consideration for the centre, not something a patient feels. For the physics in plain terms, see how Gamma Knife works.

Frame vs frameless: does CyberKnife avoid the head frame?

CyberKnife is frameless and tracks your position with imaging and a soft mask, while Gamma Knife was traditionally frame-based, fixed to the skull with four pins after four injections of local anaesthetic; but modern Gamma Knife units can also work frameless. With a frame, you feel pressure rather than pain when the pins are placed³. CyberKnife never uses pins; it re-images during treatment to correct for small movements instead.

This used to be the headline difference, and it is the one I worried about most before my own treatment. It is now less clear-cut, because Icon-generation Gamma Knife units can use a custom thermoplastic mask with cone-beam CT instead of a frame, which also lets the dose be split over a few sessions (hypofractionation)³. So frameless is no longer unique to CyberKnife. If the frame is your main concern, read frame-based versus frameless radiosurgery and, for the honest first-hand version, what the frame feels like.

Single session vs fractionated: how many visits?

Gamma Knife is usually a single day-case session, though larger targets or those near critical structures can be divided over a few; CyberKnife commonly delivers its dose over 1 to 5 sessions. A single high dose is called radiosurgery; when the dose is split into 2 to 5 fractions it is called stereotactic radiotherapy, and both machines can work either way⁴.

In practice, frame-based Gamma Knife lends itself to a single session because you would not keep a pinned frame on across several days. Mask-based Gamma Knife and CyberKnife both make fractionation straightforward, which matters when a target sits right beside the optic nerves or brainstem and the team wants to spread the dose to protect them. The number of visits, then, follows the target and the plan, not just the badge on the machine. For how the dose is worked out, see Gamma Knife planning and dose.

Cranial-only vs body and spine: what can each reach?

Gamma Knife treats intracranial targets only, roughly 5 to 40 mm in size; CyberKnife can treat the brain plus targets in the body and the spine. This is the clearest, most practical difference between the two, and often the deciding one. If the target is a small brain lesion, both are candidates; if it sits below the skull base, Gamma Knife is not an option¹.

Gamma Knife is a dedicated brain tool, and that focus is a strength for intracranial work: the whole machine is built around the head. CyberKnife trades some of that specialisation for reach across the body. For a brain target, this difference simply may not apply to you, which is why the comparison so often collapses to “which one does my centre have and trust”. For where each fits among the options, see Gamma Knife versus LINAC and proton and, more broadly, Gamma Knife versus surgery.

Do results actually differ between the two?

For a suitable brain target, the expected result is driven by the condition, the size of the target and the dose, not by which machine delivers it; both give broadly comparable radiation effect to the tissue. Take acoustic neuroma, the condition I was treated for: 5-year tumour control runs roughly 90 to 99% with a margin dose most commonly 12 to 13 Gy, and that expectation is a property of the treatment and the tumour, not of the brand¹. Hearing preservation varies widely, roughly 40 to 80%, and depends on tumour size, baseline hearing and follow-up, again independent of the machine.

I found this reassuring once I understood it. I had been treating the choice as if it were the biggest decision of the whole process, when the far more important questions were whether radiosurgery was right for my tumour at all, and what dose the team would use. The platform is a means of placing that dose accurately. For what to expect afterwards, see Gamma Knife results and follow-up, and if you are still deciding, am I a candidate for Gamma Knife and questions to ask before Gamma Knife.