Radiosurgery is a highly focused, non-invasive treatment that uses intense beams of radiation to target and destroy abnormal tissue. Although it contains the word “surgery,” the procedure does not involve a scalpel or incision, relying instead on advanced technology to deliver a concentrated dose of energy with surgical precision. The full name, stereotactic radiosurgery (SRS), highlights its reliance on three-dimensional (3D) coordinates to pinpoint the target. Radiosurgery is delivered either as a single, high-dose session or in a small number of sessions (typically two to five), which is known as fractionated SRS or Stereotactic Body Radiation Therapy (SBRT). This high-dose delivery offers an alternative for patients who may not be suitable candidates for conventional surgery.
The Physics of Precision: How Radiosurgery Works
Radiosurgery’s extreme accuracy relies on stereotactic localization, a 3D mapping system that precisely correlates an image-based target with the patient’s physical location during treatment. This technique uses sophisticated imaging, such as CT and MRI scans, to create a virtual coordinate system for the target lesion. The goal is to maximize the dose delivered to the diseased tissue while minimizing radiation exposure to surrounding healthy structures.
Dose conformity is a central concept, meaning the shape of the high-dose radiation area is tightly matched to the shape of the tumor or lesion. The treatment machine projects multiple narrow beams of radiation, each carrying a relatively low dose of energy. These beams are precisely configured to intersect at the target volume, resulting in a convergence point where the radiation dose becomes extremely high.
This intense energy triggers the biological effect by damaging the DNA within the targeted cells. Damaged DNA prevents the cells from reproducing and growing, causing them to die over time. For tumors, this cell death leads to a gradual shrinking of the mass. For vascular lesions, the radiation causes the blood vessels to thicken and eventually close off. High-dose radiation also damages the tumor’s blood supply, which further contributes to cell death.
Different Systems Used in Radiosurgery
Several distinct technological platforms are used to deliver radiosurgery, each with specific design features. The dedicated Gamma Knife system uses approximately 201 sources of Cobalt-60 to generate highly focused gamma rays. This system is primarily designed for treating intracranial lesions and requires a rigid, frame-based immobilization system fixed to the patient’s skull for sub-millimeter accuracy. The multiple fixed sources converge on a single point, making it a precise tool for small, well-defined targets in the brain.
Linear Accelerator (LINAC) based systems, such as Varian TrueBeam or Novalis, use a single radiation source to generate high-energy X-rays. These machines are highly versatile and are used for both cranial and extracranial (body) treatments. LINAC systems deliver radiation beams as the machine head rotates around the patient, often utilizing a frameless approach with a customized mask for immobilization.
Robotic systems, such as the CyberKnife, mount a miniature LINAC onto a highly flexible robotic arm. This design allows the radiation beam to be delivered from hundreds of different angles, offering exceptional dose conformity for irregularly shaped targets. The CyberKnife is known for its ability to track the movement of a target in real-time, which is important for lesions in the lung or liver that shift with breathing. It uses a frameless system and maintains accuracy through continuous X-ray imaging and robot adjustments.
Conditions Treated and The Patient Experience
Radiosurgery is an option for treating a range of medical conditions, with applications divided into intracranial and extracranial sites. Intracranial applications include benign and malignant brain tumors, such as meningiomas, acoustic neuromas, and brain metastases. It is also used for non-tumor conditions like arteriovenous malformations (AVMs), which are tangled blood vessels, and functional disorders such as trigeminal neuralgia.
When used outside the brain, the procedure targets lesions in the spine, lung, liver, and prostate, and is referred to as Stereotactic Body Radiation Therapy (SBRT). SBRT is an alternative for treating small, localized tumors that are difficult to operate on or for patients who cannot tolerate surgery. The treatment course for extracranial sites is typically fractionated, consisting of three to five sessions, while many intracranial treatments are completed in a single session.
The patient experience begins with preparation, involving detailed imaging and a collaborative treatment planning process by a team of radiation oncologists, neurosurgeons, and physicists. This planning ensures the radiation dose is optimized and precisely shaped to the target. On the treatment day, the patient is immobilized, either with a custom head frame for certain procedures or a comfortable, form-fitting plastic mask for others.
The treatment session is performed on an outpatient basis and lasts anywhere from 30 to 90 minutes. Patients are awake during the non-painful procedure and are continuously monitored by the treatment team from an adjacent control room. Recovery is swift, and most patients can resume their normal activities shortly after leaving the facility. Common short-term side effects are mild and temporary, potentially including fatigue, headache, or nausea. The full effect of the treatment, such as tumor shrinkage, occurs gradually over the following weeks or months, requiring follow-up imaging to monitor the long-term results.