Stereotactic Radiosurgery — Focused Brain Radiation

Stereotactic radiosurgery delivers a single high dose—or occasionally up to five fractionated doses—of concentrated radiation directly to an intracranial target. Specialised platforms, such as Gamma Knife, CyberKnife, or modern linear accelerators, focus hundreds of sub-millimetre radiation beams through the skull. Individually, each beam passes harmlessly through intervening brain tissue, but where they intersect, the cumulative dose becomes therapeutic.

SRS relies on rigid three-dimensional stereotactic localisation. Patients wear a lightweight immobilisation frame or customised thermoplastic mask during imaging and treatment. High-resolution magnetic resonance imaging (MRI) and computed tomography (CT) co-registration allow radiation oncologists and neurosurgeons to define target margins with sub-millimetre accuracy. This approach protects vital neural circuits, blood vessels, and cranial nerves from excessive radiation.

Discovering a brain tumour or cranial metastasis can be a deeply unsettling experience for patients and families. SRS offers a non-invasive, highly precise intervention that frequently eliminates the need for open craniotomy or prolonged inpatient hospital stays. Because SRS tightly conforms to the lesion and spares surrounding healthy cerebral tissue, it carries a substantially lower risk of cognitive impairment than traditional whole-brain radiation therapy. Recovery is rapid, usually enabling patients to return home the same day and resume systemic cancer therapies quickly, preserving valuable independence and day-to-day functional wellbeing.

Planning SRS requires high-resolution contrast-enhanced thin-slice brain MRI, often combined with stereotactic CT scans. These diagnostic studies define the exact spatial boundaries of each lesion. Although SRS is a physical technique rather than a biochemical one, tumours are guided by genomic profiling of the primary cancer (such as HER2, EGFR, or BRAF alterations), which dictates whether targeted drugs or immunotherapy will accompany radiosurgery.

SRS is most commonly used to treat brain metastases—secondary tumours that have spread to the brain from primary cancers such as lung cancer, breast cancer, malignant melanoma, renal cell carcinoma, and colorectal cancer. It is also standard therapy for benign intracranial tumours such as acoustic neuromas (vestibular schwannomas) and meningiomas, as well as selected recurrent primary brain tumours, including glioblastomas, when further operative intervention is unsuitable.

SRS has largely replaced whole-brain radiotherapy for patients with limited brain metastases, avoiding broad neurocognitive side effects. It is often combined with systemic therapies, including immune checkpoint inhibitors or targeted small molecules, which can cross the blood-brain barrier. In cases of surgically resected large brain tumours, postoperative SRS to the cavity reduces local recurrence rates. SRS can also be repeated if new small metastases appear.