What is Gamma Knife radiosurgery?

Gamma Knife radiosurgery is a non-invasive treatment that uses highly focused radiation to target the AVM.

• No incision is made.

• Multiple beams of radiation are directed precisely at the AVM.

• The radiation damages the abnormal blood vessels, causing them to gradually close off.

• The aim is to eliminate the AVM over time and reduce the risk of future bleeding.

 

Why might Gamma Knife be recommended?

The decision to recommend Gamma Knife is complex, and involves a multidisciplinary team of specialists.

Your specialist may recommend Gamma Knife if:

• The AVM is small to medium in size.

• It is located in a deep or delicate part of the brain where surgery would be too risky.

• You are not suitable for open surgery.

• Embolisation has not cured the AVM, or is being combined with radiosurgery for better results.

 

What happens during treatment?

• You will generally be aware for the treatment, which is done as a day procedure.

• You will have a lightweight frame fitted to your head to keep your head still.

• Detailed brain scans (MRI, CT, or angiography) are performed to map the AVM.

• Treatment is planned by a specialist team (neurosurgeon, radiation oncologist, radiation therapist, and physicist).

• You cannot see or feel radiation - the procedure is painless.

• You can usually go home the same day.

 

How effective is it?

• Gamma Knife radiosurgery is most effective for small to medium sized AVMs (less than 3cm in diameter).

• About 70–90% of small AVMs close completely within 2–3 years after treatment.

• Larger AVMs may need more than one treatment session or combined therapies.

• Until the AVM is fully closed, there is still a risk of bleeding. This risk is the same as the risk for an untreated brain AVM – around 2% per year for an unruptured AVM, and around 6% per year for a recently ruptured AVM.

 

What are the possible side effects and risks?

Most people tolerate Gamma Knife well, but possible risks include:

• Headache or scalp discomfort after frame fitting.

• Radiation changes in nearby brain tissue (seen on follow-up scans; rarely cause symptoms). This can occur in about 20% of patients.

• Temporary swelling in the brain, which may cause headaches, seizures, or neurological symptoms (usually treated with medication). This can occur in about 5-7% of patients.

• In rare cases, permanent neurological problems (due to radiation necrosis) can occur.

• Cyst formation after Gamma Knife is uncommon (around 3–5%) and usually develops years later (sometimes 10-20 years after Gamma Knife treatment). Most cysts do not cause symptoms, but if they do, further treatment may be needed.

 

The risks of Gamma Knife radiosurgery are often delayed, and can occur months to years after treatment.

 

Risk of radiation-induced malignancy after Gamma Knife for AVM.

• Extremely rare: The risk of developing a brain tumour (such as glioma or meningioma) due to radiation exposure from Gamma Knife is very low.

• Reported rates:

  • Large long-term studies report a risk of around 0.04% at 15 years.

  • In practical terms, that means less than 1% lifetime risk for most patients.

  • This is lower than the natural background lifetime risk of brain cancer in the general population.

• Latency (time to occurrence):

  • Radiation-induced tumours, when they occur, usually appear 10–20 years after treatment.

  • Because of this long delay, the risk is more relevant for young patients who have decades of life ahead.

 

FURTHER EXPLANATION:

The risk of developing a brain cancer following a single treatment with Gamma Knife is about 4 in 10,000 people; or put another way, if 10,000 people had Gamma Knife for a brain AVM, about 4 might develop a tumour, and 9,996 would not.

 

Recovery after Gamma Knife.

• You can usually resume normal activities within 1–2 days.

• Follow-up scans (MRI or angiogram) will be arranged regularly to check if the AVM has closed.

• It may take months to years before the AVM is completely sealed off. The average time to successful treatment is 2-3 years.

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FURTHER EXPLANATION:

To put the risks into perspective, if we treated 20 AVM patients in a year with Gamma Knife, we would expect to see about 4 patients with MRI changes due to radiation, and about 1 patient with symptomatic radiation necrosis.

We might see 1 of these patients develop a cyst 10-20 years after treatment.

We would not expect to see any of our patients develop a brain tumour as a result of the treatment.

 

Alternatives to Gamma Knife.

Not all brain AVMs are suitable for Gamma Knife treatment. Other treatment options may include:

• Microsurgical resection (open surgery to remove the AVM)

• Endovascular embolisation (blocking blood flow with glue or coils through a catheter)

• Observation (monitoring with scans if the AVM is low risk)

 

Questions to ask your doctor

• Is Gamma Knife the best option for my AVM?

• How long will it take for my AVM to close after treatment?

• What is the chance I will need further treatment?

• What side effects should I look out for?

• How often will I need follow-up scans?

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📌 Important note: This information is general and should not replace advice from your treating neurosurgeon or radiation oncologist. Always discuss your individual situation and treatment options with your specialist team.​

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