Gamma Knife continues to be the gold standard, offering unmatched precision with a fixed cobalt source, making it ideal for brain treatments. CyberKnife utilizes a robotic linear accelerator, providing versatility but with added complexity in beam targeting. ZEP-X, a newer technology, shows promise but lacks sufficient clinical data. The choice of technology depends on patient needs, but Gamma Knife stands out due to its simplicity, safety, and long track record in treating brain tumors.

Shahid Akhter, Editor, Healthyouonline, spoke to Dr. Dheerendra Prasad, Chief, Gamma Knife Radiosurgery and Medical Director, Radiation Medicine at Roswell Park, Buffalo, NY, to explore the key differences between CyberKnife, ZEP-X, and Gamma Knife.

Radiosurgery once threatened operative surgery? What changed?

Radiosurgery was initially met with skepticism by neurosurgeons, many fearing it would replace microsurgery. However, the evolution has been quite the opposite. Over time, the best synergy emerged—surgeons now choose what’s best for the patient.

Many surgical procedures once considered the only option often resulted in good tumor control but poor patient outcomes. Radiosurgery has allowed neurosurgeons to tailor procedures, stopping when it's safest and treating residual tumors with precision. For small targets, open neurosurgery has become unnecessary.

Gamma Knife: Evolution

The Gamma Knife exemplifies this precision. While it doesn’t physically cut, it operates with the accuracy of a scalpel—one-third of a millimeter—a level of precision unmatched in deep brain procedures.

Despite its long history, Gamma Knife remains the gold standard due to its unmatched accuracy. Its core principle—delivering precise, high-dose radiation—has remained unchanged, even as its planning, monitoring, and patient positioning technologies have advanced.

Today, semi-automation and robotic placement have streamlined treatments, making them smoother for both patients and operators. Gamma Knife remains the only platform that seamlessly integrates CT scans, MRIs, angiograms, PET scans, and even molecular imaging.

Additionally, while immunotherapy is a breakthrough in cancer treatment, its efficacy significantly increases when combined with radiosurgery, further cementing the role of Gamma Knife in modern treatment protocols.

Gamma Knife vs. CyberKnife vs. ZAP-X

ZAP-X, like CyberKnife, uses a single radiation source and a linear accelerator. In the case of CyberKnife, the source is mounted on a robotic arm, whereas in ZAP-X, it is mounted on a gyroscope. The Gamma Knife, on the other hand, uses very small beam geometry—192 beams initially configured in a crossfire pattern. This can be mimicked by using a single source and moving it around the patient, whether on a robotic arm (as in CyberKnife) or in a gyroscopic setup (as in ZAP-X).

However, these alternatives still rely on a single beam, which limits the number of directions, angles of incidence, and crossfire beams available. While it is possible to create a similar-looking dose plan with all these technologies, adding complexity through moving sources introduces challenges in verification and patient positioning.

Gamma Knife inherently resolves these challenges due to its fixed-source, fixed-geometry design. Additionally, the beam energy from its cobalt source is at 1 million electron volts, producing a sharp dose gradient. This means that the radiation sharply falls off outside the target, minimizing damage to surrounding tissues—something no other technology can match.

While all three technologies can achieve dose delivery to a target, the key difference lies in how they handle doses outside the target area. For patients, particularly those with benign tumors who are expected to live for decades after treatment, reducing unnecessary radiation exposure is critical for quality of life.

ZAP-X is a relatively new technology, with only a few installations worldwide—one in the U.S., a few in Europe, and one in India, with more expected in the future. However, there is not yet enough clinical data to compare its effectiveness against established technologies like Gamma Knife or CyberKnife.

Gamma Knife has treated over a million patients worldwide, while CyberKnife has treated several hundred thousand. CyberKnife has been a versatile tool for brain, spine, and other applications, whereas ZAP-X refocuses solely on brain treatments. However, ZAP-X remains unproven in terms of long-term outcomes.

Jon Adler, the designer of ZAP-X, is known for his contributions to radiosurgery. While ZAP-X is expected to be a good technology and will likely improve over time, it is still evolving. Its software continues to improve, but whether it will surpass Gamma Knife remains uncertain.

Ultimately, Gamma Knife remains the gold standard due to its simplicity, which translates to safety. While it may appear to be a simple device, this simplicity has withstood the test of time, with decades of successful treatments and low complication rates.

Gamma Knife: Enhancing Quality of Life

The integration of Gamma Knife radiosurgery into microsurgery has significantly improved patients' quality of life. For those with large benign tumors requiring surgical debulking, surgeons can now operate up to a point where the patient retains function while avoiding life-threatening complications. The remaining tumor can then be treated with Gamma Knife, reducing the need for extensive surgery.

For smaller benign tumors, Gamma Knife eliminates the need for open surgery entirely, sparing patients from hospital stays and associated risks. This enhances safety and recovery time, making treatment far less invasive.

In the past, brain cancer meant whole-brain radiotherapy, which, while effective, caused significant cognitive decline over time. Patients often lost their ability to remember and function as they once did. As survival rates improved with chemotherapy and immunotherapy, the focus shifted from just disease control to preserving patient identity and quality of life.

Gamma Knife recommended for children

A striking example is the NHS in England, which has strictly approved Gamma Knife as the only radiosurgery option for children. This decision stems from Gamma Knife’s superior precision, which minimizes collateral damage, ensuring long-term safety for young patients who may live for decades.

Despite misconceptions about cobalt radiation, Gamma Knife is exceptionally safe. The amount of cobalt-60 used is minimal—comparable to a small salt shaker—and significantly less than industrial sterilization equipment. When properly managed, it remains the safest option for both patients and operators while posing virtually no risk to the public.