Gamma Knife: for which brain conditions is stereotactic radiosurgery indicated?

Gamma Knife: radiosurgery, not open surgery

The term “Gamma Knife” can be misleading: there is no blade and, in most treatments, the skull is not opened. It is a stereotactic radiosurgery platform that concentrates many radiation beams on a target inside the skull. Each individual beam delivers a limited dose to the tissues it passes through, while their convergence makes it possible to deliver a high and very precise dose to the target.

How is it decided whether a lesion can be treated?

The decision depends on the diagnosis, the size, the number of lesions, their location, their proximity to the optic nerves or brainstem, the presence of a mass effect, symptoms, age, general health and treatments already received. The ASTRO guidelines on brain metastases support stereotactic radiosurgery for selected patients, but a large tumour causing compression may lead to open surgery being discussed.

Possible indications, depending on the case, include certain brain metastases, vestibular schwannomas, certain meningiomas, certain arteriovenous malformations and other intracranial lesions. Radiosurgery may also be discussed for certain neurological pain conditions such as trigeminal neuralgia. The words “Gamma Knife” are therefore never an indication in themselves: the diagnosis and the multidisciplinary strategy remain central.

For a vestibular schwannoma, size, hearing, compression of the brainstem and symptoms guide the choice between monitoring, radiosurgery and surgery. For an arteriovenous malformation, radiosurgery is mainly intended for small lesions or those located in areas where surgery is risky; its effect is delayed and the risk of bleeding is not removed immediately.

How does the treatment work?

The pathway generally involves very high-precision imaging and a stereotactic immobilisation system, depending on the platform and the indication. The target and the organs to be protected are outlined, then a dose plan is calculated. The patient is then positioned on the machine. The radiation itself is painless; it is mainly the immobilisation, the duration or anxiety that some patients may find uncomfortable.

Depending on the system, immobilisation may use a stereotactic frame attached to the skull under local anaesthetic or, for certain indications, a mask. The details should be explained by the centre before treatment.

What happens afterwards?

Many patients go home quickly or after a short period of observation, but follow-up is essential. Radiosurgery does not act like the immediate removal of a mass: a tumour may shrink slowly or simply stop growing; a vascular malformation may take months or years to close. Follow-up MRI scans are therefore scheduled.

What are the risks and limits?

The effects depend on the area treated and the dose: tiredness, headaches, temporary swelling, temporary worsening of symptoms or, more rarely, radiation necrosis. Corticosteroids may be prescribed in certain situations. A lesion that is too large, compression requiring decompression or the absence of a tissue diagnosis may make another strategy more appropriate.

Neighbouring tissues receive a lower dose than the target, but not zero. A neurosurgical emergency or a target that is too diffuse also lead to other treatments being preferred: the platform should never be chosen simply because it is available.

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