What is gamma knife surgery?

Gamma Knife Surgery: A Precision Radiation Treatment

Gamma Knife surgery is a non-invasive stereotactic radiosurgery technique that delivers highly focused beams of ionizing radiation with submillimeter precision to treat intracranial lesions while sparing surrounding normal tissues. 1

Definition and Technology

• Gamma Knife is a specialized device developed in 1951 by Leksell at the Karolinska Institute in Stockholm, Sweden, consisting of approximately 200 cobalt-60 sources arranged in a helmet-like configuration that produce gamma rays with an average energy of 1.25 MeV 1
• The patient's head is secured with a stereotactic frame to achieve precise targeting, allowing for mechanical accuracy within 0.5 mm 2
• The 201 gamma beams intersect at a focal point with accuracy within 0.3 mm, creating a sharply circumscribed lesion in a single treatment session 2

How It Works

• Gamma Knife surgery uses a stereotactic fixation system and noncoplanar convergent beams that create a very sharp peripheral dose fall-off at the target edge 1
• The steep dose gradient minimizes radiation exposure to nearby critical structures while delivering a single large fraction of ionizing radiation to kill tumor cells 1
• The effects of radiosurgery are mediated through non-selective direct axonal damage with no vascular occlusion or thrombosis, with post-irradiation changes established by six months post-treatment 1

Alternative Platforms

• Linear accelerator (LINAC)-based systems can also deliver stereotactic radiosurgery, with the gantry moving in space to change the delivery angle 1
• CyberKnife is a specific type of LINAC-based system that delivers similar submillimeter accuracy without requiring a stereotactic frame, using an image guidance system with kilovolt images before each beam delivery 1
• No platform has demonstrated superiority over another; the primary factor in successful SRS is correct application by treating physicians 1

Clinical Applications

• Treatment of brain tumors, including benign meningiomas (90% control rate at 3 years) and metastatic tumors (87% showing rapid regression) 3
• Management of arteriovenous malformations 2
• Treatment of trigeminal neuralgia, with approximately 80% of patients achieving significant pain relief 4
• Treatment of vestibular schwannomas (acoustic neuromas) 1
• Management of paragangliomas with tumor control rates of 88-100% 1

Effectiveness for Trigeminal Neuralgia

• Complete pain relief is initially achieved in approximately 75% of trigeminal neuralgia patients, with about 50% maintaining this outcome at three years 1
• Pain relief typically occurs within three months after treatment 1
• Results are better when used as primary treatment in patients with typical trigeminal neuralgia symptoms 1
• A minimum radiosurgical dose of 70 Gy delivered to a 4 mm target at the sensory root of the trigeminal nerve is recommended 1

Complications and Side Effects

• Sensory disturbance is the most frequent complication, with new or increased facial paresthesias developing in approximately 10-49% of patients treated for trigeminal neuralgia 4, 5
• During the procedure, 2% of patients may experience anxiety or syncopal episodes 6
• Other potential complications include headaches, facial pain, motor deficits, hydrocephalus, and seizures 6
• The severity of trigeminal nerve dysfunction may improve in about one-third of affected patients over time 5

Advantages Over Traditional Surgery

• Minimally invasive alternative to open microsurgery 6
• Requires a short hospital stay compared to traditional neurosurgical procedures 1
• Provides immediate relief of pain in most patients with trigeminal neuralgia 1
• Lower risk of complications compared to open surgical procedures 1

Limitations

• Most effective for smaller tumors (maximum diameter <3 cm) 1
• Not risk-free, with potential for radiation injury 6
• For trigeminal neuralgia, outcomes are comparable to other ablative techniques but not superior to microvascular decompression for long-term pain relief 7
• Current data on effectiveness are largely observational with generally poor quality reporting 1

Gamma Knife surgery represents an important treatment option for patients with various intracranial conditions, particularly when traditional surgery carries high risks or is not feasible.