Stereotactic Radiosurgery (SRS)

Introduction

If a doctor has recommended stereotactic radiosurgery (SRS), you may be feeling a mix of relief and concern. The word “radiosurgery” sounds dramatic, but SRS does not involve cutting, stitches, or opening the skull. It is a form of radiation treatment that uses many narrow beams to deliver a strong, precise dose to a small target — most often inside the brain.

This article is written for people who have already been told that SRS is a possibility, or who are now planning treatment. It explains what SRS is, the conditions it is used for, how doctors plan and deliver the treatment, what the day itself is like, and what to expect in the weeks and months afterwards. It also covers the different machines used (such as Gamma Knife and CyberKnife), side effects, and how doctors follow up to check how well the treatment has worked.

Throughout the article, we describe what current practice and major professional societies — including the American Society for Radiation Oncology (ASTRO), the International Stereotactic Radiosurgery Society (ISRS), and similar groups — consider standard care. Your own treatment plan will be shaped by your specific diagnosis, imaging, and the multidisciplinary team caring for you.

What Is Stereotactic Radiosurgery?

Stereotactic radiosurgery (SRS) is a way of delivering radiation that is very different from traditional radiation therapy. The word “stereotactic” means using a three-dimensional coordinate system to find a target very precisely — in this case, a small abnormality inside the brain or, in selected cases, the spine.

In SRS, dozens or hundreds of thin radiation beams are aimed at the target from different angles. Each individual beam is weak and passes through normal tissue without doing much harm. Where the beams cross at the target, the doses add up to a high, biologically powerful dose. This is what allows SRS to damage abnormal cells while keeping the dose to surrounding healthy brain tissue low.

Despite the word “surgery,” SRS does not involve:

• Incisions or stitches
• Opening the skull
• General anaesthesia, in most adult cases
• A hospital stay, in most cases

SRS is usually given in a single session, which is what most clearly sets it apart from other radiation techniques. When the same precision approach is used over 2 to 5 sessions, it is called fractionated stereotactic radiotherapy (FSRT or SRT). When the same idea is applied to tumours outside the brain — such as in the lung, liver, or spine — it is usually called stereotactic body radiation therapy (SBRT).

How SRS Differs from Other Radiation Treatments

• Conventional external beam radiation therapy (EBRT): delivered in many small daily sessions over several weeks, often to larger areas.
• Intensity-modulated radiation therapy (IMRT): a refined form of EBRT that shapes beam intensity to spare normal tissue; usually still given over multiple weeks.
• Image-guided radiation therapy (IGRT): the use of imaging during treatment to confirm accuracy. SRS uses IGRT as part of its precision system.
• Stereotactic body radiation therapy (SBRT): the same precision principle applied outside the brain, usually in 1 to 5 sessions.

Some Terms You May Hear

• Gray (Gy): the unit used to measure radiation dose.
• Fraction: a single radiation session. SRS is usually a single fraction; FSRT uses a small number of fractions.
• Target volume: the precise region being treated, mapped on imaging.
• Organs at risk: nearby healthy structures, such as the optic nerves or brainstem, that the team works to protect.

Why Is SRS Performed?

SRS is used when doctors need to treat a small, well-defined target in or near the brain — or sometimes the spine — while limiting damage to the surrounding tissue. It is most often considered when open surgery is risky, when the target is in a hard-to-reach area, or when a focal radiation dose offers a clear benefit. The decision is usually made by a multidisciplinary team that includes a radiation oncologist, a neurosurgeon, and a medical physicist, often with input from a neuro-oncologist or neurologist.

Brain Tumours

• Brain metastases: tumours that have spread to the brain from cancers elsewhere in the body (such as lung, breast, or melanoma). For people with a limited number of brain metastases, current guidelines from groups such as ASTRO and NCCN describe SRS as a standard option, often preferred over whole-brain radiation because it spares cognitive function.
• Meningiomas: usually benign tumours that grow from the membranes covering the brain. SRS is commonly used for small or moderate-size meningiomas, or for residual tumour after surgery.
• Vestibular schwannomas (acoustic neuromas): benign tumours on the nerve to the inner ear. SRS is a well-established alternative to open surgery for small and medium-sized tumours.
• Pituitary tumours: for selected tumours not fully controlled by surgery or medication.
• Selected gliomas and recurrent primary brain tumours: in specific situations, usually after multidisciplinary review.

Vascular Conditions

• Arteriovenous malformations (AVMs): abnormal tangles of blood vessels in the brain. SRS can gradually cause the abnormal vessels to close off over 1 to 3 years, lowering the risk of bleeding.
• Cavernous malformations: in carefully selected cases.

Functional Neurological Conditions

• Trigeminal neuralgia: a severe facial pain condition. SRS targeted at the trigeminal nerve can give long-lasting pain relief for many patients when medications fail or surgery is not suitable.
• Selected movement disorders: in some centres, SRS may be considered for tremor when other approaches are not options.

Spinal Lesions (Selected Cases)

Stereotactic radiation can also be used for tumours of the spine and spinal cord region, particularly spinal metastases. In the spine, this is most often described as SBRT or spine SRS. The principles are the same: a high, focused dose to a small target, with careful protection of the spinal cord.

Who Is a Candidate for SRS?

Whether SRS is appropriate for a particular person is a clinical decision based on imaging, the type and behaviour of the lesion, and the patient’s overall situation. In general, factors that make SRS a reasonable option include:

• A small, well-defined target (often up to about 3 cm, though this varies by condition and centre)
• A target in a location where open surgery would be high-risk — for example, deep in the brain or close to important structures
• A limited number of lesions (for example, a small number of brain metastases)
• Overall health that makes lengthy daily radiation or major surgery less suitable
• A clear treatment goal, such as local control of a tumour, pain relief, or AVM closure

SRS may be less suitable when:

• The lesion is very large or poorly defined
• There are many lesions and whole-brain radiation or systemic treatment may be more appropriate
• Significant surrounding swelling or mass effect means that surgical removal is needed urgently
• Previous radiation to the same area limits how much additional dose can be safely delivered

Pregnancy is generally a contraindication to brain SRS unless there is no safer alternative, and the team will discuss this carefully if relevant.

Alternatives to SRS

Depending on the condition, alternatives may include:

• Open or microsurgical resection: for tumours that are accessible and where tissue is needed for diagnosis, or where decompression is urgent.
• Whole-brain radiation therapy (WBRT): for people with many brain metastases. Current guidelines from groups such as ASTRO have shifted towards using SRS for limited brain metastases when feasible, because of better cognitive outcomes.
• Fractionated stereotactic radiotherapy (FSRT): when a target is too large or too close to sensitive structures for a single high dose, the same precision approach is delivered in a few sessions.
• Conventional external beam radiation therapy (EBRT) or IMRT: for larger or more diffuse targets.
• Observation with serial imaging: for some small, slow-growing benign lesions (such as small meningiomas or vestibular schwannomas), watchful waiting with regular MRI may be appropriate.
• Medical therapy: for trigeminal neuralgia (medications such as carbamazepine), pituitary tumours (hormone-blocking medications), and metastases (systemic cancer therapy).
• Endovascular treatment or microsurgery: for AVMs, depending on size and location.

SRS can be delivered using several different machines. All work on the same basic principle — many narrow beams converging on a precise target — but the technology, immobilisation, and treatment time can differ. The choice of system often depends on the equipment available at the centre, the condition being treated, and the team’s experience.

Gamma Knife

Gamma Knife is one of the oldest and most established SRS systems. It uses many tiny beams of gamma radiation from cobalt sources, all aimed at a single point. It is dedicated to treating targets in the head and upper neck. Traditionally, it has been used with a rigid frame fixed to the skull with pins under local anaesthesia, though newer models can also use a removable mask for fractionated treatments. Gamma Knife is widely used for vestibular schwannomas, small meningiomas, brain metastases, AVMs, and trigeminal neuralgia.

CyberKnife

CyberKnife uses a small linear accelerator mounted on a robotic arm that moves around the patient. Image guidance tracks the target in real time, which means it can adjust if there is small movement. A custom thermoplastic mask is used for the head, rather than a fixed frame. CyberKnife can treat targets in the brain, spine, and elsewhere in the body, and it is often used when treatments are delivered over a few sessions.

LINAC-based SRS

Many modern radiation centres deliver SRS using a standard linear accelerator (LINAC) adapted with specialised software, collimators, and image guidance. Examples include systems sometimes branded as Novalis, TrueBeam STx, Edge, and similar. These machines can deliver SRS to the brain and SBRT to the body. They typically use a thermoplastic mask for head treatments.

Fractionated Stereotactic Radiotherapy (FSRT)

When the target is too large for a single high dose, or when it is very close to sensitive structures like the optic nerves or brainstem, the same precision approach can be split into 2 to 5 sessions. This is called fractionated stereotactic radiotherapy. It keeps the precision of SRS but spreads the dose, which can lower the risk of injury to nearby tissue.

From the patient’s point of view, the differences between Gamma Knife, CyberKnife, and LINAC-based SRS are smaller than they may appear. All are recognised by major professional societies. The most important factor is the experience of the team and the quality of the treatment plan.

Preparing for SRS

Once SRS is planned, the preparation phase is detailed and may take several days. The goal is to map the target with millimetre accuracy so the radiation can be delivered safely.

Consultation and Review

You will meet with a radiation oncologist, and often a neurosurgeon, who will review your imaging, medical history, and previous treatments. They will explain why SRS is being considered, the expected benefit, and the possible side effects. This is a good time to ask questions and to share concerns about medications, allergies, or claustrophobia.

Imaging

High-quality imaging is the foundation of SRS planning. You will typically have:

• A high-resolution MRI of the brain with contrast
• A planning CT scan
• For AVMs, sometimes a cerebral angiogram
• For functional conditions, specialised MRI sequences

• A stereotactic head frame, which is attached to the skull with small pins under local anaesthesia. It stays on for the day of treatment and is removed afterwards.
• A custom thermoplastic mask, made by warming a sheet of plastic and shaping it to your face. The mask is comfortable enough to wear during treatment and is reusable for fractionated sessions.

The team will tell you which system they use and what to expect.

Medications and Practical Preparation

• You may be asked to stop or adjust certain medications. Tell the team about all medications, including herbal supplements and blood thinners.
• You may be asked to fast for a few hours before treatment, particularly if sedation is planned.
• Wear comfortable, loose clothing on the day. Avoid hair products, makeup, or jewellery on the treatment area.
• Arrange for someone to accompany you. Even when sedation is not used, having a companion is helpful.
• If you have a pacemaker, defibrillator, or other implant, tell the team in advance.

Treatment Planning Behind the Scenes

Once imaging is complete, the radiation oncologist, medical physicist, and dosimetrist work together — sometimes over several days — to design the treatment plan. They decide the precise dose, the number and angles of beams, and the way the dose is shaped to match the target while sparing organs at risk. This work is invisible to you, but it is one of the most important parts of SRS.

What Happens During SRS

On the day of treatment, you will arrive at the radiation oncology department and check in. The exact sequence varies by system, but a typical day looks like this:

Arrival and Setup

• You change into a gown and any final imaging is performed.
• If a frame is being used, it is fitted under local anaesthesia. You may feel pressure and brief pinching, but the area is numbed.
• If a mask is being used, it is placed and secured to the treatment table.
• The team uses imaging to confirm that you are positioned exactly as planned.

The Treatment Itself

• You lie still on the treatment couch. You remain awake in most cases.
• The machine moves around you. With some systems, the couch may also move.
• You do not feel the radiation. There is no heat, no pain, and no smell.
• You can usually hear the machine and speak with staff through an intercom.
• Depending on the system and the complexity of the plan, the treatment can take anywhere from about 30 minutes to a few hours.

After the Session

• The frame or mask is removed.
• If a frame was used, the small pin sites are cleaned and dressed. Minor tenderness and small skin marks are normal and settle quickly.
• You are observed for a short time. Most people go home the same day.
• You are not radioactive. It is safe to be around family, including children and pregnant people.

For fractionated treatments, the daily sessions are usually shorter, because most planning has already been done.

Recovery and Aftercare

Recovery after SRS is usually quick compared with open surgery. Most people resume normal daily activities within a day or two. However, the biological effect of the radiation unfolds gradually over weeks and months, so “recovery” means more than just the day after treatment.

The First Few Days

• Mild fatigue is common and may last a few days.
• A mild headache can occur, particularly if a frame was used. Simple pain relief usually helps.
• Scalp tenderness at frame pin sites is normal and resolves quickly.
• Some people feel mildly nauseated; this is usually short-lived.
• You can typically eat, drink, shower, and move normally.

The First Few Weeks

• Fatigue may continue intermittently.
• You may be prescribed a short course of steroids (such as dexamethasone) to reduce swelling, particularly if the target is in an area sensitive to inflammation.
• Driving restrictions depend on your condition (such as whether you have had seizures) and your local rules.
• Most people return to work within a few days to two weeks, depending on the nature of their job and their underlying condition.

Longer-Term Healing

• Tumours may shrink slowly over months to years. Many stay stable rather than disappearing.
• AVMs typically take 1 to 3 years to close off after treatment.
• Trigeminal neuralgia pain relief may take weeks to develop.
• Symptoms of pituitary tumours may improve gradually as the tumour shrinks.

This delayed effect is a normal part of how SRS works. The team will follow you with imaging and clinical reviews to track progress.

Follow-Up Imaging

Follow-up usually includes:

• An MRI scan a few months after treatment, then at regular intervals
• Clinical reviews with the radiation oncologist, neurosurgeon, or neuro-oncologist
• Specialist tests when relevant (for example, hearing tests after treatment for vestibular schwannoma, hormone testing after pituitary SRS, or angiography for AVMs)

The follow-up schedule is tailored to the condition and may continue for several years.

Risks and Side Effects

SRS is generally well tolerated, but no radiation treatment is risk-free. Side effects are divided into early effects (in the first weeks) and late effects (months to years later).

Common Early Side Effects

• Fatigue
• Mild headache
• Mild nausea
• Scalp tenderness or small areas of hair thinning where beams entered the skin (uncommon and usually temporary)
• Brief worsening of existing neurological symptoms due to swelling, which often improves with steroids

Less Common Side Effects

• Seizures, particularly in people who have had seizures before or whose target is in a seizure-prone area
• Temporary worsening of weakness, balance problems, or speech changes, depending on the target location
• Hearing changes (for example, with vestibular schwannoma treatment)
• Hormonal changes (for example, after pituitary treatment)
• Facial numbness (for example, after trigeminal neuralgia treatment)

Late and Rare Complications

• Radiation necrosis: a delayed reaction where treated tissue becomes inflamed and damaged, sometimes months to a year or more after SRS. It can cause headaches and neurological symptoms and may be treated with steroids or, occasionally, other interventions.
• Delayed neurological changes: uncommon, depending on the area treated.
• Secondary tumours: very rarely, radiation can lead to a new tumour many years later. The absolute risk is small.
• Cyst formation: reported after some AVM treatments, years later.

The team weighs these risks against the expected benefit when recommending SRS, and will explain what is most relevant in your specific situation.

When to Contact the Team Urgently

After SRS, contact your team if you develop:

• A new or worsening severe headache
• A seizure
• New weakness, numbness, or trouble speaking
• Vision changes
• Persistent vomiting
• Fever or signs of infection at frame pin sites

Success Rates and Outcomes

Outcomes after SRS depend strongly on what is being treated, the size and location of the target, and the patient’s overall health. Major professional societies and large clinical studies describe several broad patterns:

• For small, well-defined brain metastases, SRS achieves high rates of local control — meaning the treated lesion stops growing or shrinks.
• For vestibular schwannomas and small meningiomas, long-term control rates are high, and most patients keep stable function over many years.
• For AVMs, the chance of complete closure depends on size and dose, and is highest for small AVMs. Closure typically takes 1 to 3 years.
• For trigeminal neuralgia, many patients experience significant pain relief, although it may take several weeks to develop and may not be permanent.

“Success” for SRS often means local control rather than a complete disappearance of the lesion on imaging. Your radiation oncologist can give you a personalised estimate based on your specific diagnosis and imaging.

Stereotactic Radiosurgery in Children

SRS can be used in children, though it is considered carefully because the developing brain is more sensitive to radiation. Common situations include selected brain tumours, vascular malformations such as AVMs, and certain refractory conditions when other options have been weighed.

Specific considerations in children include:

• Anaesthesia: younger children often need sedation or general anaesthesia to stay still during imaging and treatment.
• Immobilisation: a mask is often preferred over a head frame.
• Long-term effects: because children have a longer life ahead of them, the team pays particular attention to limiting dose to healthy brain tissue, protecting cognitive development, hormonal function, and reducing the small long-term risk of secondary tumours.
• Alternatives: in many paediatric situations, surgery, chemotherapy, or proton therapy may be considered alongside or instead of SRS, and decisions are made in a paediatric multidisciplinary team.

Parents are usually closely involved at every step, and the paediatric radiation oncology team will explain how the treatment will be adapted for their child.

Life After SRS

Most people return to their usual routine soon after SRS. The longer-term picture depends on the underlying condition.

Going Back to Normal Activities

• Light activities can usually resume within a day or two.
• Work, school, exercise, and social activities can often be resumed within a few days to two weeks, guided by how you feel and by any restrictions from your team.
• Driving depends on your underlying condition and local rules. Discuss this with your doctor.
• Air travel after SRS is usually safe within days, but check with your team, particularly for international travel.

Emotional Adjustment

Even though SRS is non-invasive, it is still a serious medical treatment. It is common to feel a mix of relief, anxiety about results, and uncertainty in the waiting months. Talking with family, joining a support group, or speaking with a counsellor can help. If you experience persistent low mood, sleep problems, or anxiety, tell your team — support is part of good follow-up care.

Ongoing Treatment for the Underlying Condition

SRS treats a specific target. It does not replace other treatments needed for the underlying disease:

• People with cancer that has spread to the brain usually continue systemic treatment under their oncology team.
• People with pituitary tumours may continue hormone monitoring and replacement.
• People with AVMs may need imaging follow-up for years until closure is confirmed.
• People with trigeminal neuralgia may continue medications, often at lower doses, as relief develops.

Frequently Asked Questions

Is SRS actually surgery?

No. SRS uses focused radiation rather than instruments to treat a target. There are no incisions, stitches, or skull opening. The word “surgery” reflects the precision of the dose, not the technique.

Will I feel the radiation?

No. Radiation cannot be felt during delivery. You may feel pressure from the frame or mask, hear the machine, and feel the couch move, but you will not feel the radiation itself.

Will I lose my hair?

Most people do not lose noticeable hair, because the beams pass through different parts of the scalp from many angles. In some cases, a small patch of thinning may appear where beams entered, and this usually grows back. Targets close to the skin can carry a higher chance of hair changes.

Will I be radioactive after treatment?

No. SRS uses radiation that passes through and is absorbed by the tissue at the target. You are not radioactive. It is safe to hug family members, including children, and to be around pregnant people.

How long does it take to know if the treatment worked?

SRS works gradually. Imaging changes may not be clear for several months. AVMs may take 1 to 3 years to close. Trigeminal neuralgia pain relief can take weeks. Your team will arrange follow-up MRI scans and clinical reviews at appropriate intervals.

Can SRS be repeated?

In some situations, repeat SRS or a different radiation approach can be considered, depending on how much dose the surrounding tissue has already received and how the target has responded. This is a decision for the treatment team.

Is SRS the same as Gamma Knife or CyberKnife?

Gamma Knife and CyberKnife are two of the machines used to deliver SRS. SRS can also be delivered on modern linear accelerators (LINACs). The underlying principle is the same: many beams converging on a precise target.

What if my tumour is too large for SRS?

Larger or irregular targets may be treated with fractionated stereotactic radiotherapy (FSRT) over a few sessions, with conventional radiation therapy, or with surgery first to reduce size. The team will discuss what fits best.

Can I have an MRI after SRS?

Yes. MRI is the main way SRS results are followed and is usually safe after treatment.

How long is the follow-up?

Follow-up depends on the condition. For benign tumours and AVMs, imaging often continues for several years. For metastases, follow-up is integrated with overall cancer care. Your team will lay out the schedule.

Conclusion

Stereotactic radiosurgery is a precise, non-invasive way of delivering a focused radiation dose to a small target in the brain or, in selected cases, the spine. For many people with brain metastases, benign brain tumours, AVMs, or trigeminal neuralgia, it offers an effective option that avoids open surgery and is usually completed in a single session.

The strength of SRS lies in detailed planning and teamwork — radiation oncologists, neurosurgeons, medical physicists, and other specialists working together to design and deliver the treatment. Recovery is typically quick, but the biological effect unfolds over months, so follow-up imaging and clinical reviews are an important part of the process.

Whether SRS is the right choice in a particular situation, which delivery system is most suitable, and how it fits with other treatments are all decisions made together with the treating team, based on imaging, diagnosis, and the patient’s goals. Understanding what SRS is and how it works can make those conversations clearer and help you take part in them with confidence.