Stereotactic Radiosurgery: Advancing Precision in Treating Neurological Disorders

Stereotactic radiosurgery (SRS) is a transformative medical technology that has reshaped how certain neurological disorders are treated. Unlike traditional radiation therapy, which is diffuse and often requires multiple sessions, SRS delivers highly focused radiation to specific targets in the brain or spine, sparing surrounding healthy tissue.

This precision has made SRS an essential tool in treating both benign and malignant conditions. Over the years, advancements in SRS platforms and techniques have broadened its applications, offering hope to patients with conditions that were once considered difficult or impossible to manage. We consider it one of the most important tools we have available to us at Cleveland Clinic.

What is Stereotactic Radiosurgery?

SRS is often described as “precision-targeted radiation.” I often compare the technology to a glove fitting a hand, able to conform to the shape of specific targets while sparing surrounding tissue. Unlike conventional radiation therapy, which delivers lower doses of radiation across a broader area over multiple sessions, SRS operates more like a surgical intervention, delivering high doses in one or a few sessions. This targeted approach minimizes damage to healthy tissue and maximizes the effectiveness of treatment.

Another analogy that I sometimes use: traditional radiation therapy is akin to spreading weed killer across a field, while SRS is like plucking individual dandelions. This distinction is particularly important when dealing with sensitive structures such as the brain and spinal cord, where preserving normal tissue is critical to maintaining neurological function.

Platforms for Radiosurgery

SRS technology has evolved significantly since its inception. One of the most common platforms for brain radiosurgery is the Gamma Knife, which has been widely recognized for its precision in targeting brain lesions. The Gamma Knife machine, often described as resembling a large commercial hairdryer, is specifically designed for treating brain disorders and is considered one of the most exacting tools available for this purpose.

For radiosurgery for areas outside the brain, such as the spine, linear accelerator-based systems such as Edge are commonly used. These systems offer similar precision but are tailored to different anatomical and clinical needs. The choice of platform depends on the location of the lesion, the size, and the specific condition being treated.

The Role of Immobilization

One of the critical components of SRS is immobilization, which ensures that the target remains stationary during treatment. Historically, patients undergoing Gamma Knife radiosurgery required a minimally invasive head frame to achieve this level of control. However, advancements in technology have allowed for non-invasive alternatives, such as masks, which are now used for approximately 70% of patients.

The decision to use a frame or mask depends on the specific condition being treated and the need for immobilization. For example, conditions such as trigeminal neuralgia, where the target is extremely small, may still require the use of a head frame to ensure accuracy.

Further Applications of Stereotactic Radiosurgery

SRS has proven effective in treating a wide range of benign and malignant neurological disorders. Among its most common applications is the treatment of brain metastases, which often present as multiple lesions. SRS allows for highly accurate targeting of each lesion without affecting surrounding healthy brain tissue. Other applications include vascular abnormalities, such as arteriovenous malformations (AVMs). These tangles of blood vessels can pose significant risks, including hemorrhagic strokes, and radiosurgery offers a non-invasive way to manage them effectively.

Benign tumors, such as vestibular schwannomas and meningiomas, can also be treated using SRS, as well as certain primary brain tumors such as glioblastomas in select cases. SRS is also used for functional disorders, such as trigeminal neuralgia. By targeting the trigeminal nerve with directed radiation, SRS can provide relief of patients’ facial pain without invasive surgery.

Collaboration in Radiosurgery

The effective delivery of SRS requires a multidisciplinary approach involving neurosurgeons, radiation oncologists, medical physicists, radiation therapists, and specialized nursing staff. Each member of the team plays a vital role in ensuring the safety and success of the procedure. Neurosurgeons often focus on identifying and targeting the lesion, while radiation oncologists deliver the proper dose of radiation. Medical physicists ensure that the treatment plan is technically feasible and is executed properly.

This collaborative approach is particularly important when determining the best course of treatment. For example, decisions about whether to use whole-brain radiation or SRS for brain metastases depend on factors such as the number and size of lesions, and the patient’s overall health. While whole-brain radiation may be appropriate for patients with extensive disease, SRS is often preferred for those with fewer lesions to minimize neurocognitive side effects.

Expanding Applications: Spine Radiosurgery

SRS has also been adapted for use in treating spinal conditions, although the approach differs from brain radiosurgery in several ways. Spinal metastases often affect the bone rather than the spinal cord itself, and the challenge lies in delivering a high enough dose to the tumor while sparing the delicate spinal cord. Immobilization techniques and dose constraints are critical to achieving this balance.

In some cases, patients with spinal tumors may undergo a procedure known as separation surgery before radiosurgery. This minimally invasive surgical technique creates space between the tumor and the spinal cord, allowing for safer delivery of high-dose radiation. This approach has reduced the need for extensive surgeries that were once common in managing spinal tumors.

Advancements in Radiosurgery Techniques

As SRS technology continues to evolve, we are exploring new ways to enhance its effectiveness. Fractionated and staged radiosurgery are two emerging techniques that offer promising results for larger brain tumors. Fractionated radiosurgery involves delivering radiation over several consecutive days, while staged radiosurgery treats the lesion in multiple sessions spaced weeks apart. These approaches allow for better control of larger tumors while minimizing side effects.

Another area of research involves repeat radiosurgery for patients whose tumors recur after initial treatment. Understanding how to deliver additional doses of radiation safely and effectively is an ongoing challenge, but early results suggest that repeat radiosurgery can provide durable control in select cases.

Challenges and Future Directions

While SRS has revolutionized the treatment of many neurological disorders, challenges remain. For example, glioblastomas remain difficult to treat with radiosurgery alone. Researchers are working to identify specific nests of tumor cells that can be targeted with high-dose radiation, offering hope for improved outcomes in this area.

Another area of focus is pediatric radiosurgery. Treating children with SRS requires special considerations, such as the use of anesthesia for immobilization and careful attention to dosing to avoid unexpected toxicities. Despite these challenges, SRS has shown promising results in managing pediatric conditions such as sarcomas and AVMs.

Conclusion

SRS represents a significant advancement in the treatment of neurological disorders. Its precision, efficacy, and ability to spare healthy tissue make it a valuable tool for managing conditions ranging from brain metastases to vascular abnormalities and functional disorders. As technology continues to improve and research expands, the potential applications of SRS are likely to grow, offering hope to patients with complex and challenging conditions.

While the field still faces challenges, particularly in treating diffuse and aggressive tumors such as glioblastomas, the progress made in recent years is undeniable. SRS has not only improved outcomes for many patients but also enhanced their quality of life by offering non-invasive outpatient treatment options with minimal side effects. As this technology evolves, it will undoubtedly play an even greater role in the future of neurosurgery and radiation oncology.

Lilyana Angelov is the Director of Cleveland Clinic’s Gamma Knife Center and Head Section of Spine Tumors.