Gamma Knife for Brain Tumours: Which Tumours It Treats and Which It Does Not

Gamma Knife treats small, well-defined brain tumours that can be dosed precisely without opening the skull, both benign ones such as acoustic neuroma and meningioma and malignant secondary tumours such as brain metastases, rather than any single tumour type. It is not a treatment for every brain tumour. What decides suitability is the size, the position, and how clear the tumour’s edge is, not the diagnosis on its own¹.

When my acoustic neuroma was found, the first thing I wanted to know was whether other people with other tumours were being sent for the same treatment, and why some were and some were not. This is the umbrella view I pieced together: how benign and malignant, and primary and secondary, tumours fit into radiosurgery, and where the line falls. For the whole treatment in one place, start with Gamma Knife radiosurgery; if you want to know whether your own tumour qualifies, read am I a candidate for Gamma Knife.

Which brain tumours does Gamma Knife treat?

Gamma Knife treats brain tumours that are small, have a clear edge, and sit where a focused dose can be shaped safely, which in practice means a defined list of conditions rather than “brain tumours” as a whole. As a rule of thumb, single-session radiosurgery suits targets around 3 to 3.5 cm or smaller (about 10 to 15 cc in volume); larger ones are staged over a few sessions or sent to surgery².

The common tumour types, each with its own article, are the benign nerve-sheath and covering tumours (acoustic neuroma, meningioma), the hormone-related pituitary tumours, and the malignant deposits that have spread from elsewhere (brain metastases):

• Acoustic neuroma (vestibular schwannoma): benign, 5-year tumour control of roughly 90 to 99%. See Gamma Knife for acoustic neuroma.
• Meningioma (benign, grade I): 5-year local control of roughly 85 to 100%. See Gamma Knife for meningioma.
• Pituitary adenoma: tumour control over 90%. See Gamma Knife for pituitary adenoma.
• Brain metastases: malignant, 1-year local control of roughly 70 to 90%. See Gamma Knife for brain metastases.

Benign versus malignant brain tumours

The benign and malignant distinction changes what radiosurgery is trying to do: for a benign tumour the aim is long-term control of a slow-growing lump, while for a malignant one it is local control of a fast-changing deposit within a broader cancer plan. Benign tumours such as grade I meningioma and acoustic neuroma respond slowly, and 5-year control commonly runs from 85 to 100% depending on the tumour³.

Malignant tumours are different in tempo and in context. For brain metastases, 1-year local control is roughly 70 to 90%, strongly dependent on the dose delivered, and radiosurgery is one part of a plan run by the wider oncology team rather than a standalone cure¹. Higher-grade meningiomas (grade II and III) also behave more aggressively, and their control after radiosurgery is markedly worse than the benign grade I figures. Where a tumour sits on the benign to malignant scale is one of the first things the team weighs.

I remember being relieved to hear “benign”, and then having to learn that benign did not mean harmless or that it could be left alone; it meant slow, and treatable, and worth controlling. For how that decision is framed, see watch and wait versus Gamma Knife.

Primary versus secondary brain tumours

A primary brain tumour starts in the brain or its coverings, while a secondary (metastatic) tumour has spread to the brain from a cancer elsewhere, and Gamma Knife is used for well-defined tumours in both groups. Primary tumours suited to radiosurgery are largely the benign, well-circumscribed ones: acoustic neuroma, meningioma, pituitary adenoma. Secondary tumours are the brain metastases that arrive from cancers such as lung or breast⁴.

For secondary tumours, the modern approach favours treating a limited number of deposits individually with focused radiosurgery, sparing the rest of the brain. Older guidance capped this at about four metastases per session; high-volume practice now treats more, guided by the total tumour volume rather than a simple count². That shift, from counting lesions to measuring total volume, is why some people with several deposits are still offered focal treatment. For the detail, see Gamma Knife for multiple brain metastases and the comparison in Gamma Knife versus whole-brain radiotherapy.

Which brain tumours does Gamma Knife not treat?

Gamma Knife is not used for large tumours, diffuse tumours with no clear edge, or tumours that are causing dangerous pressure and need rapid relief, because a focused single-target dose cannot cover them or cannot act fast enough. Diffuse gliomas, including glioblastoma, spread finger-like into the surrounding brain, so there is no crisp target to aim the beams at; these are treated with surgery, fractionated radiotherapy and chemotherapy instead⁴.

Surgery is generally preferred when the tumour is over about 3.5 cm, when it is pressing on the brain and pressure must be relieved quickly, or when the team needs a tissue sample (a biopsy) to know exactly what they are dealing with. Tumours sitting right against the optic nerves or brainstem may instead have the dose split over a few sessions to protect those structures¹. In short:

• Too large: over roughly 3.5 cm; staged, fractionated, or operated on instead.
• No clear edge: diffuse gliomas including glioblastoma are not radiosurgery targets.
• Rapid pressure relief needed: surgery removes the bulk quickly.
• Diagnosis unknown: surgery or biopsy gives tissue that radiosurgery cannot.

For the full candidacy picture see am I a candidate for Gamma Knife, and for when the operating theatre wins, Gamma Knife versus surgery.

How results differ by tumour type

Radiosurgery works gradually and its results depend heavily on the tumour type, so a benign acoustic neuroma and a malignant metastasis follow very different timelines even after the same day-case treatment. Across benign brain tumours the target usually stays visible on scans, changing over 1 to 3 years; control, not disappearance, is the aim³.

The numbers make the point. Benign meningioma and acoustic neuroma reach 5-year control of roughly 85 to 100% and 90 to 99% respectively, while brain metastases are measured at 1 year, around 70 to 90% local control, because the wider cancer sets the longer horizon. Because the tumour lingers on early imaging, the follow-up scan schedule matters more than how quickly you feel back to normal. I found the slow, invisible nature of it the hardest thing to trust: nothing looked different for a long time. For that side of it, see Gamma Knife results and follow-up and radiosurgery and scanxiety.

Who decides which tumours suit Gamma Knife?

A multidisciplinary team decides, looking at your actual imaging: a neurosurgeon, a radiation oncologist and a medical physicist weigh the tumour’s size, position and type before recommending radiosurgery, surgery, or watching and waiting. The dose itself is then planned by that team while you wait, which takes one to several hours depending on the target².

This is the part I understated to myself at first. I assumed radiosurgery was automatically the gentler and therefore better choice for my acoustic neuroma; in fact the team weighed it against surgery and against simply monitoring before recommending it, and the reasoning was specific to my scan, not to the diagnosis label. No website, including this one, can make that call for a particular tumour⁵. For what to ask when it is your turn, see questions to ask before Gamma Knife.