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Gamma Knife Radiosurgery

Non-Invasive Stereotactic Radiosurgery for Brain Tumours, AVM, Acoustic Neuroma, and Trigeminal Neuralgia at Shree Hospitals

Gamma Knife radiosurgery is one of the most precise treatments in all of medicine. Using 192 individual cobalt-60 gamma radiation beams, each aimed at a single focal point within the brain with sub-millimetre accuracy, the Leksell Gamma Knife delivers a precisely shaped, high-dose radiation treatment to a brain target - a tumour, vascular malformation, or pain circuit - while the surrounding normal brain tissue receives only a small fraction of the total dose (because only the beams' focal point receives the full combined dose). The result is a highly effective, non-invasive (no incision, no general anaesthesia) treatment that destroys the target with millimetre precision. At Shree Hospitals, Gamma Knife radiosurgery is delivered by a specialist team of neurosurgeons, radiation oncologists, and medical physicists with extensive SRS (stereotactic radiosurgery) experience for a range of indications.

What is Gamma Knife Radiosurgery and How Does It Work?

Stereotactic radiosurgery (SRS) is the delivery of a very high, precisely focused dose of radiation to a small target within the brain in a single session (or a small number of sessions), using multiple convergent beams each aimed at the same point from different directions. The Leksell Gamma Knife (Elekta AB) - the original and most widely used SRS device - uses 192 fixed cobalt-60 gamma radiation sources, each producing a narrow gamma ray beam, all focused on a single isocenter (focal point). At the isocenter, all 192 beams converge and their doses add, creating a very high dose at the target. At any point outside the isocenter, only a small number of beams pass through that point, creating a much lower dose. The steep dose gradient at the edge of the treatment volume means that tissue just 2 to 3mm outside the target receives dramatically less radiation than the target itself. This makes the Gamma Knife enormously precise and allows high-dose treatment of brain targets adjacent to critical structures such as the brainstem, optic nerves, and cranial nerves.

The treatment mechanism differs between indications. For brain tumours (metastases, meningioma): the high radiation dose (15 to 24Gy in a single session for metastases; 12 to 15Gy for meningioma) causes direct tumour cell DNA double-strand breaks leading to tumour cell death, tumour shrinkage, and ultimately stabilisation or disappearance of the treated lesion. For AVM (arteriovenous malformation): the radiation dose (16 to 25Gy to the nidus) causes progressive thickening of the AVM vessel walls over 2 to 3 years, leading to gradual obliteration of the abnormal vessels. For acoustic neuroma (vestibular schwannoma): the dose (11 to 13Gy to the 50% isodose) controls tumour growth (prevents enlargement) in over 90% of cases at 10 years. For trigeminal neuralgia: a very high focal dose (70 to 90Gy) to the trigeminal nerve root entry zone (REZ) near the brainstem produces pain relief in 70 to 85% of patients within 3 to 6 months.

At Shree Hospitals, every Gamma Knife treatment is planned and delivered by a dedicated SRS team comprising the neurosurgeon (responsible for frame placement and clinical decision-making), the radiation oncologist (responsible for dose prescription and tumour targeting), and the medical physicist (responsible for treatment planning - designing the optimal beam arrangement using GammaPlan software to deliver the prescribed dose to the target while minimising dose to adjacent structures). All Gamma Knife cases are reviewed at the Neuro-Oncology MDT before treatment. Pre-treatment MRI (with and without gadolinium, using thin-cut stereotactic MRI sequences) and CT with stereotactic fiducials are used for target definition and treatment planning.

Who Is Gamma Knife Radiosurgery For?

• Brain metastases: 1 to 10 lesions, each under 3 to 4cm - Gamma Knife SRS achieves local control of 80 to 90% of treated lesions and is preferred over whole brain radiotherapy for patients with limited brain metastases and controlled systemic disease
• Meningioma: WHO Grade I (benign) meningiomas in surgically challenging locations (skull base, cavernous sinus, posterior fossa) or residual after subtotal resection
• Acoustic neuroma (vestibular schwannoma): tumours under 3cm causing hearing loss, tinnitus, and balance problems - 90%+ tumour control at 10 years with hearing preservation in most patients
• AVM (arteriovenous malformation): small (under 3cm nidus) unruptured or previously bled AVMs - obliteration in 60 to 80% at 3 years
• Pituitary adenoma: residual or recurrent non-functioning adenoma after surgery; functioning adenomas (acromegaly, Cushing's) in patients not responding to medical therapy
• Trigeminal neuralgia: medically refractory, classical Type 1 neuralgia in older patients or those unfit for microvascular decompression

Is Gamma Knife Radiosurgery Right for You?

• The target is small enough (under 3 to 3.5cm for most indications) for safe SRS - larger targets require surgical resection or fractionated radiotherapy
• The target is surgically high risk due to location (brainstem, deep nuclei, eloquent cortex, cavernous sinus) or patient fitness
• The patient has multiple brain metastases (up to 10 treated lesions in some protocols) that cannot all be surgically removed
• The patient cannot undergo general anaesthesia (Gamma Knife requires only a frame under local anaesthesia)
• The patient has already had maximum surgical resection and requires post-operative SRS to the surgical bed for local control
• For AVM: the lesion is in an eloquent or deep location where surgical resection carries unacceptable neurological risk

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Our Approach to Gamma Knife Radiosurgery

At At Shree Hospitals, every Gamma Knife treatment is delivered by an expert multidisciplinary SRS team - neurosurgeon, radiation oncologist, and medical physicist - working together from case selection through treatment planning to post-treatment follow-up.

Patient Selection and MDT Case Review

All Gamma Knife cases are reviewed at the Neuro-Oncology (or appropriate MDT) before treatment is confirmed. The case selection criteria are applied rigorously: target volume (must be appropriate for SRS), number of targets, proximity to critical structures (optic chiasm receives no more than 8Gy in SRS dose constraints; brainstem no more than 12Gy), patient performance status and systemic disease status (for metastases), and whether prior surgery or fractionated radiotherapy has already been given to the same area (which changes dose tolerance). The decision between single-session SRS and hypofractionated SRS (2 to 5 fractions, used for larger targets, targets adjacent to optic apparatus, or re-irradiation) is made at the MDT.

Stereotactic Frame Placement and Imaging

On the day of treatment, the Leksell stereotactic frame (a rigid aluminium frame) is fixed to the patient's skull under local anaesthesia using four skull pins inserted through small local anaesthetic skin blebs. The frame is the coordinate system that defines the spatial relationship between the patient's skull and the target within the brain - it allows the Gamma Knife to target the lesion with sub-millimetre accuracy. After frame fixation, the patient undergoes gadolinium-enhanced MRI (thin-cut 1mm volumetric sequences) and CT with the frame in place. For AVM, digital subtraction angiography (DSA) is added to define the AVM nidus for precise targeting. The MRI and CT (and DSA if used) are fused in the GammaPlan treatment planning system.

Treatment Planning (GammaPlan)

The neurosurgeon and radiation oncologist identify and contour the treatment target(s) and the adjacent critical structures (optic nerves, optic chiasm, brainstem, cochlea, hippocampus) on the planning MRI. The medical physicist then designs the treatment plan using the GammaPlan software - selecting the optimal combination of isocenters (focal points), shot sizes (different collimator apertures: 4mm, 8mm, or 16mm), and beam-on-times to create a highly conformal dose distribution that covers the target at the prescribed isodose (usually the 50% isodose line) while maintaining the dose to adjacent critical structures below established tolerance constraints. Plan quality is assessed using conformality index (how well the high-dose volume matches the target) and gradient index (how steeply the dose falls off at the target edge). The plan is reviewed and approved by the full SRS team before treatment.

Top Neurosurgeons in Mumbai

Every specialist at Shree Hospitals is MCh Neurosurgery board-certified with over 15 years of clinical experience in awake craniotomy, brain tumour surgery, neuronavigation, fluorescence-guided resection, functional brain mapping, and neuro-oncology.

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