WHAT IS STEREOTACTIC RADIOSURGERY
AND HOW IS IT DIFFERENT FROM REGULAR RADIATION?
Stereotactic radiosurgery uses precision radiation to destroy tumours in 1–5 sessions — no incision, no surgery, no general anaesthesia. The word "surgery" is misleading; SRS is radiation therapy delivered with surgical precision, aiming to ablate rather than gradually shrink a tumour.
analyticsAt a Glance
- check_circle1–5 sessions vs 20–40 for conventional radiotherapy — same or better local control
- check_circleNo surgery, no anaesthesia, no incision — treatment sessions of 15–60 minutes each
- check_circleExtremely tight margins (1–2 mm) spare surrounding normal tissue from high doses
- check_circleEstablished for brain metastases, acoustic neuroma, meningioma, AVM, spinal tumours, and more
The Critical Difference: Dose per Fraction
The fundamental difference between SRS and conventional radiotherapy is not the radiation itself — both use X-rays or gamma rays — but how the dose is distributed across time and precisely directed in space.
“Conventional radiotherapy gives the tumour 2 Gy per day for 5–6 weeks, allowing normal tissue to repair between fractions. SRS gives 15–25 Gy in a single session, destroying the tumour before it can repair — relying entirely on extreme spatial precision to spare normal tissue rather than on the repair process.”
Conventional Radiotherapy: Exploiting Repair
Standard radiotherapy delivers 1.8–2.0 Gy per fraction, 5 days per week, for 20–40 fractions. The low dose per fraction allows normal cells — which repair radiation damage more efficiently than cancer cells — to recover between sessions. Tumour cells accumulate DNA damage with each fraction. This repair difference is the radiobiological rationale for fractionation.
SRS: Bypassing Repair Through Precision
SRS delivers 12–25 Gy in a single session (or 5–9 Gy × 3–5 fractions for SBRT). At these doses, tumour cell death is predominantly through direct DNA double-strand breaks and vascular damage — mechanisms that overwhelm even efficient DNA repair. Normal tissue protection is achieved not through repair but through extreme spatial precision — the high dose field matches the tumour shape with 1–2 mm accuracy, dropping sharply at its edges.
How Surgical Precision Is Achieved Without Surgery
SRS precision is built from four technical components working together — each contributing to the millimetre-level accuracy that defines the treatment.
Immobilisation: Removing Movement
The patient's head (for intracranial SRS) or body (for SBRT) is immobilised in a precisely reproducible position. For Gamma Knife: a stereotactic frame is screwed to the skull under local anaesthesia. For frameless systems (CyberKnife, TrueBeam): a thermoplastic mask or body mould. Immobilisation ensures the tumour position during treatment matches the planned coordinates.
High-Resolution 3D Imaging: Mapping the Target
Pre-treatment MRI (1–1.5 mm slices), CT, and/or PET precisely define the tumour's three-dimensional shape and position relative to surrounding critical structures. The radiation oncologist manually delineates the target volume and organs at risk. This planning data drives the radiation delivery computer.
Multi-Beam Convergence: Distributing Dose
SRS delivers radiation from multiple non-coplanar angles (or in a continuous arc) that converge on the tumour. Each individual beam carries low dose; only at the convergence point — inside the tumour — does the dose summate to the ablative level. This is the geometric basis for the sharp dose fall-off at the tumour margin.
Image-Guided Delivery: Real-Time Verification
Modern SRS systems verify patient position immediately before and during treatment using on-board imaging (kV X-ray, cone-beam CT, or robotic tracking). CyberKnife uses continuous image tracking throughout delivery. Any movement beyond tolerance pauses treatment until repositioning occurs.
SRS vs Conventional Radiotherapy: Head-to-Head
A structured comparison across the dimensions that matter most for patients choosing between SRS and conventional fractionated radiotherapy.
SRS Advantages
- Fewer Sessions1–5 sessions vs 20–40 — dramatically less disruption to daily life.
- Higher Local Control for Small TargetsFor well-defined small tumours (<3–4 cm), SRS achieves 85–95% local control rates — matching or exceeding surgery and conventional RT.
- No Surgery RequiredNo incision, no anaesthesia, no hospital stay, no surgical recovery.
- Reirradiation PossibleExtremely precise dose distribution allows treatment in previously irradiated fields where conventional RT cannot safely be repeated.
- Minimal Time BurdenEach session 15–60 minutes. A course completed in 1–5 days total.
Conventional RT Advantages
- Better for Large TumoursConventional RT handles larger tumour volumes more safely — SRS is limited to lesions typically <3–4 cm (brain) or per SBRT protocols for body sites.
- Normal Tissue Repair ExploitedFractionation specifically protects normal tissue through repair — safer for tumours adjacent to critical serial structures (spinal cord, optic chiasm).
- Wider AvailabilityLinear accelerators for conventional RT exist at far more centres than SRS-capable systems.
- Larger Evidence Base for Some IndicationsDecades of fractionated RT data for many tumour types that lack SRS RCT evidence.
- Better for Infiltrative TumoursDiffuse or infiltrative tumours with no clear margin cannot be precisely targeted by SRS — fractionated RT treats a larger field more safely.
Established SRS and SBRT Indications
Tumour types and conditions for which SRS/SBRT has established evidence and regulatory/guideline support.
| Indication | SRS / SBRT | Evidence Level | Typical Dose |
|---|---|---|---|
| Brain metastases (1–10) | SRS | Multiple phase III RCTs; standard of care | 15–24 Gy single fraction |
| Acoustic neuroma (vestibular schwannoma) | SRS | Large prospective series; preferred for medium-sized | 11–13 Gy single fraction |
| Meningioma (grade I) | SRS | Large series; guideline-supported | 12–16 Gy single fraction |
| Arteriovenous malformation (AVM) | SRS | Large prospective series; guideline-supported | 18–25 Gy single fraction |
| Pituitary adenoma | SRS | Established; preferred for recurrent/residual | 14–20 Gy single fraction |
| Early NSCLC (inoperable stage I) | SBRT | Phase II/III trials; NCCN standard | 48–54 Gy in 3–4 fractions |
| Prostate cancer (localised) | SBRT | Phase III non-inferiority (PACE-B); growing standard | 36.25 Gy in 5 fractions |
| Spinal metastases | Spine SRS / SBRT | Strong prospective data; pain and cord decompression | 16–24 Gy in 1–3 fractions |
| Liver tumours (HCC, CRC mets) | SBRT | Growing evidence; alternative to ablation | 45–60 Gy in 3–5 fractions |
| Trigeminal neuralgia | SRS | Established; preferred non-surgical option | 70–90 Gy to Gasserian ganglion |
Explore the SRS Knowledge Base
Related SRS topics and resources.
- Gamma Knife vs CyberKnife vs TrueBeam: How to Choose
- SRS for Brain Metastases: The Evidence That Changed Standard of Care
- SRS vs WBRT: Understanding the Neurocognitive Trade-Off
- SRS for Acoustic Neuroma: Radiation Over Surgery
- Lung RFA for Early-Stage NSCLC and Pulmonary Metastases
- Stereotactic Radiosurgery — Full Treatment Page
Frequently Asked Questions
Common questions about what SRS is.
About SRS
Is SRS the same as SBRT?
SRS and SBRT (stereotactic body radiotherapy) use the same precision principles and delivery technology, but differ by anatomical site. SRS specifically refers to stereotactic treatment of intracranial targets (brain, skull base). SBRT refers to the same high-dose precision approach applied to body (extracranial) targets — lungs, liver, spine, prostate, kidney, and other sites. Some systems and clinicians use the terms interchangeably; technically the site distinguishes them.
If SRS is radiation, why is it called "surgery"?
The term "radiosurgery" was coined by neurosurgeon Lars Leksell in the 1950s to describe the intent: using radiation to produce a sharp, well-defined lesion with surgical precision, in a single session, analogous to a surgical excision. The "surgery" refers to the precision and ablative intent — not to any incision or physical intervention. The name has persisted despite being technically misleading. Modern SRS systems are entirely non-invasive; the most an intracranial frame-based system requires is local anaesthesia for frame pin placement.
How CancerFax Helps
CancerFax is a specialist cancer access and patient-navigation platform. We help patients and families understand their options, organise medical records, coordinate hospital communication, and support cross-border treatment planning where appropriate.
We help collect and organise reports, scans, pathology, biomarker results, and treatment history for structured case review.
We communicate with hospitals or trial teams to assess whether a case may be suitable for further screening.
We support appointment coordination, document submission, translation, and direct communication with international departments.
For international patients, we help with practical coordination — travel planning, hospital admission guidance, and local support.
If this option is not suitable, we help explore other relevant treatments, clinical trials, or advanced care pathways.
From inquiry through to follow-up, our coordinators provide a single point of contact for the family.
CancerFax does not guarantee treatment access, eligibility, or clinical outcome. Our role is to help patients access accurate information, structured review, and appropriate specialist pathways.
Is SRS Appropriate for Your Tumour?
Upload your MRI/CT imaging and medical history. Our radiation oncology team will assess whether SRS is appropriate and identify the most experienced SRS centre for your specific case.
For informational purposes only. SRS suitability requires evaluation by qualified radiation oncology specialists.