Stereotactic Radiosurgery System

Stereotactic radiosurgery (SRS) treats a target of up to a few centimetres with a single high dose, or with two to five high doses in what is called hypofractionated radiosurgery. The same principle applied outside the brain is called stereotactic body radiotherapy (SBRT) or stereotactic ablative radiotherapy (SABR). This page covers platforms designed only for this work, with Gamma Knife and CyberKnife M6 as examples of the two main designs. One design places around two hundred small cobalt sources in a shielded unit, all aimed at a single point inside the head, and treats targets in the brain. The other mounts a compact linear accelerator on a robotic arm that can approach the target from many directions, and treats the brain, spine and body. Both are run by a team of radiation oncologists, neurosurgeons and medical physicists.

Planning starts with detailed imaging, usually a thin-slice MRI and a CT scan, sometimes with angiography for vascular malformations. The team outlines the target and nearby sensitive structures such as the optic nerves and brainstem, and a physicist calculates how many small beams should overlap so the dose concentrates in the target. On a cobalt-based unit your head is held still by a light frame fixed to the skull under local anaesthetic or by a fitted mask, and imaging confirms the position. A robotic-arm system needs no frame: it takes repeated X-ray images during the session and corrects its aim for small movements, including breathing motion for lung or liver targets. A LINAC-based radiosurgery service reaches similar accuracy in another way, using a general-purpose machine with a fine multileaf collimator, cone-beam imaging and a precisely adjustable couch, and it also delivers everyday radiotherapy between radiosurgery cases.

In the brain, radiosurgery treats metastases, often several at once, as well as benign tumours such as meningiomas, vestibular schwannomas (acoustic neuromas) and pituitary adenomas. It can close arteriovenous malformations over time and relieve the facial pain of trigeminal neuralgia when medicines no longer help, and some centres use it for selected movement disorders such as tremor. It may also treat a tumour that remains or returns after surgery. Outside the brain, frameless platforms treat spine metastases, early lung cancers in people who cannot have surgery, and selected liver, kidney, pancreatic and prostate tumours. It generally suits targets of up to about three to four centimetres; larger tumours, or tumours pressing on vital structures, may need surgery or conventional radiotherapy instead. A neurosurgeon or radiation oncologist decides after reviewing your scans.

The main benefits are precision, no incision and a short course of treatment. Most people are treated as outpatients, return to normal activities within a day or two and can often fly home a few days later. Early side effects can include tiredness, headache, nausea or soreness at the frame pin sites, and steroids are sometimes given to reduce swelling. Later effects depend on the target and dose: swelling or tissue damage in the treated area, called radiation necrosis, can appear months later and may need treatment. The result is not immediate. Benign tumours usually stop growing rather than disappear, malformations may take one to three years to close, and pain relief for trigeminal neuralgia can take weeks to months.