Radiosurgery (Gamma Knife/CyberKnife)

Stereotactic radiosurgery delivers a single, high, conformal dose of focused radiation to a precisely defined intracranial target while sparing surrounding tissue, achieving an ablative or growth-arresting effect without an open operation. Platforms such as the Gamma Knife and the robotic CyberKnife realize the same stereotactic principle using converging beams of radiation rather than a surgical instrument.

Definition

Stereotactic radiosurgery is the delivery of a precisely targeted, typically single-session high dose of ionizing radiation to a defined intracranial volume using stereotactic localization, producing a controlled biological effect on the target while minimizing dose to adjacent structures.

Scope

This entry covers the concept of focused-radiation ablation, the major delivery platforms, common indications such as metastases and vestibular schwannomas, and the dose-control trade-off. It is a reference-educational overview and does not provide dosing or treatment guidance.

Core questions

• How does focused radiation achieve a surgical effect without an incision?
• How do Gamma Knife and CyberKnife platforms deliver conformal dose?
• For which intracranial targets is radiosurgery an established option?
• What is the trade-off between marginal dose, tumour control, and adjacent-tissue injury?

Key concepts

• Conformal single-session dose
• Marginal (tumour-margin) dose
• Gamma Knife and CyberKnife platforms
• Tumour control versus complication risk
• Stereotactic localization of the target
• Non-invasive ablation

Mechanisms

The target is localized stereotactically and many low-intensity radiation beams are arranged to converge on it, so that a high, conformal dose is concentrated within the target volume while each individual beam path receives comparatively little. Tumour or lesion control is governed by the dose delivered to the margin of the target, and the central trade-off of the technique is between a dose high enough to control the lesion and one low enough to limit injury to adjacent neural and vascular structures.

Clinical relevance

Radiosurgery is an established non-invasive option for selected brain metastases, benign tumours such as vestibular schwannomas and meningiomas, vascular malformations, and certain functional targets, often where open surgery is unsuitable. This entry explains the technique and how its outcomes are reported; it describes the evidence and is not guidance for individual treatment.

Evidence & guidelines

Randomized evidence includes RTOG 9508 (Andrews et al., 2004), which showed that adding a stereotactic radiosurgery boost to whole-brain radiotherapy improved outcomes for selected patients with limited brain metastases. Observational series describe radiosurgery for vestibular schwannoma, including the relationship between marginal dose and tumour control with reduced cranial-nerve morbidity at 12-13 Gy (Flickinger et al., 2003) and long-term tumour control and quality-of-life outcomes after Gamma Knife treatment (Wangerid et al., 2014).

History

Radiosurgery originated within stereotactic neurosurgery as a way to treat deep targets without opening the skull, applying the coordinate-frame concept to converging radiation beams (Gildenberg, 2009). The Gamma Knife and later robotic linear-accelerator systems such as CyberKnife extended the approach to a wide range of intracranial targets.

Seminal works

• andrews-2004
• flickinger-2003

Frequently asked questions

Is radiosurgery actually surgery?

Despite the name, it involves no incision; it concentrates many converging beams of radiation on a stereotactically defined target to produce an ablative or growth-controlling effect, usually in a single session.

What is the difference between Gamma Knife and CyberKnife?

Both deliver stereotactic radiosurgery but use different hardware: the Gamma Knife uses fixed cobalt radiation sources, while the CyberKnife is a robotically mounted linear accelerator; both aim to deliver conformal dose to the target.