Radiosurgery is an advanced, non-invasive treatment method that uses precisely focused, high-energy radiation to target diseased tissues. Despite its name, this is not a surgical procedure and does not involve an incision, anesthesia, or a recovery period typical of conventional surgery. The term “surgery” refers to the treatment’s extremely high precision and the definitive outcome it aims to achieve in one or a few sessions. This technique is formally known as Stereotactic Radiosurgery (SRS) when applied to the brain and spine, or Stereotactic Body Radiation Therapy (SBRT) for other areas of the body. Radiosurgery delivers a high radiation dose to a small, well-defined target, making it an effective alternative for patients who may not be suitable candidates for traditional surgery.
The Mechanism of Highly Focused Radiation
The foundational principle of radiosurgery involves the convergence of multiple, narrow radiation beams at a single, precisely defined point inside the patient called the isocenter. Individually, each beam passes through healthy tissue with minimal effect, but where all the beams intersect, the cumulative dose of radiation becomes lethal to the target tissue. This technique creates a very steep dose fall-off, meaning the radiation intensity drops sharply just outside the target volume, which protects surrounding healthy tissues.
The high-energy radiation, typically X-rays or gamma rays, works by damaging the deoxyribonucleic acid (DNA) within the targeted cells. This damage prevents the cells from successfully growing and dividing. Over time, the cell’s inability to repair this extensive damage triggers programmed cell death (apoptosis) or, in some cases, necrosis.
Radiosurgery is distinguished from conventional radiation therapy by its use of a high dose delivered in a single session or a few sessions (hypofractionation). Conventional radiotherapy uses many small doses spread out over several weeks. The high-dose approach of radiosurgery is designed to completely destroy the target tissue, often achieving a result similar to a surgical resection.
Key Technologies Used in Radiosurgery Delivery
The precision required for radiosurgery is achieved through specialized delivery systems, each using a distinct method to generate and direct the radiation beams.
The Gamma Knife is a dedicated system that uses up to 201 radioactive cobalt-60 sources to emit gamma rays. This system is predominantly used for treating targets within the head. It relies on a rigid, frame-based immobilization system fixed to the skull to ensure sub-millimeter accuracy.
Linear Accelerator (LINAC)-based systems are the most common and versatile technology used for radiosurgery. These machines generate high-energy X-rays and can treat targets anywhere in the body, capable of both SRS for intracranial targets and SBRT for extracranial sites. LINAC systems achieve precision through image-guidance and patient immobilization using custom-molded thermoplastic masks.
The CyberKnife is a specific type of LINAC mounted on a highly maneuverable robotic arm. This design allows the system to deliver radiation beams from thousands of angles, offering exceptional dose conformity for irregularly shaped targets. The CyberKnife uses real-time image-guidance to track the target position and adjust the robot’s movement continuously, allowing for the treatment of moving targets in the lung or liver without a rigid head frame.
Primary Conditions Treated
Radiosurgery is widely applied in neuro-oncology and for certain non-malignant conditions, primarily due to its exceptional accuracy in delicate areas. Intracranial treatments are the most common application, targeting both cancerous and non-cancerous brain tumors, including metastases and primary tumors like meningiomas. The treatment aims to stop tumor growth or cause the lesion to shrink over time.
Vascular malformations, such as Arteriovenous Malformations (AVMs)—tangles of abnormal blood vessels in the brain—are also frequently treated. The high radiation dose causes the walls of these blood vessels to gradually thicken and close off, a process that can take one to three years, lowering the risk of hemorrhage. Radiosurgery is also a standard option for functional disorders, such as trigeminal neuralgia, by creating a small lesion on the trigeminal nerve to block pain signals.
When applied to the rest of the body, the technique is known as SBRT. SBRT delivers a high ablative dose over two to five treatments, providing a highly effective, non-surgical option for tumors that are small, localized, or difficult to reach surgically. This body application relies heavily on advanced imaging and tracking to account for organ motion. SBRT extends its use to tumors in the:
- Lung
- Liver
- Pancreas
- Spine
The Patient Experience
The radiosurgery process begins with diagnostic imaging, typically involving an MRI or CT scan, to precisely map the target area. This imaging data is loaded into a computerized planning system, where the treatment team designs a plan to optimize the radiation dose to the target while sparing surrounding structures.
During the treatment session, the patient is positioned on the treatment couch and immobilized to prevent any movement that could compromise accuracy. Depending on the technology used, this may involve a rigid head frame temporarily fixed to the skull or a custom-fitted thermoplastic mask. While the frame offers the highest stability, the mask is often preferred by patients for comfort, especially when combined with real-time tracking systems.
The treatment itself is relatively short, often lasting from 30 to 90 minutes. Since there is no incision, patients typically return home the same day and can resume normal activities shortly afterward. The therapeutic effects are not immediate; tumor shrinkage or vessel closure occurs gradually over the following weeks, months, or even years as the radiation-damaged cells slowly die off.