Stereotactic Radiosurgery: A Noninvasive Treatment Option

Mayo Clinic has performed radiosurgery in Rochester, Minnesota since 1990. With nearly 4,000 patients treated to date, it has one of the busiest radiosurgery practices in the world. All 3 Mayo campuses offer stereotactic radiosurgery, and the treatment teams include neurosurgeons, radiation oncologists, and medical physicists with specialized training in radiosurgical case management. Patients range in age from toddlers to the elderly.

Stereotactic radiosurgery is the single-session, focused delivery of radiation to an image-defined intracranial target. Used as an alternative to or in conjunction with traditional neurosurgery, radiosurgery is an excellent noninvasive option for a number of conditions.

Distinguishing Radiosurgery From Radiotherapy

Radiosurgery is sometimes confused with radiotherapy. Both deliver radiation but use different mechanisms and dosing regimens to minimize the chance of radiation damage to healthy tissue. Radiotherapy delivers low doses of radiation over time in multiple treatment sessions. Radiosurgery delivers radiation in highly conformal dose plans with steep fall-off. This allows safe delivery of higher doses of radiation so that the entire dose is administered in a single session. For some patients, such as those with large arteriovenous malformations or large skull base tumors, radiosurgery may be performed in multiple sessions over several months. In such cases, the target is divided into several smaller targets, each of which is addressed with the same total high-radiation dose, but in separate sessions until the radiation coverage is complete.

Expanding Radiosurgery Practice

At the Mayo Clinic campuses in Arizona and Florida, radiosurgery is conducted using a linear accelerator with an image-guided targeting system that allows the delivery of focal radiation as either a single, 1-time dose or a hypofractionated regimen (1 time per day for 5 days). The radiation source moves around the patient.

At Mayo Clinic in Minnesota, the Gamma Knife (Elekta Instrument AB, Stockholm, Sweden) is used. Beams of radiation are delivered through holes in a collimator unit or helmet. The beams are arranged in a circular array and converge on a central target. The radiation source remains stationary, and the patient is positioned to accommodate radiation delivery. The Rochester campus has expanded its practice in stereotactic radiosurgery with the acquisition of new equipment that will open radiosurgery to new applications.

The next generation of Gamma Knife, called the Leksell Gamma Knife Perfexion, was installed at the Minnesota campus. It expands Mayo Clinic's radiosurgery practice to include treatment of head and neck cancers as well as ocular disorders (neoplasms and macular degeneration), peripheral skull base carcinomas, and tumors of the upper cervical spine. The new instrument increases accuracy and precision in radiation delivery, improves patient comfort, and reduces treatment time up to 60%.

Gamma Knife

Enlarge

Discussing the new Gamma Knife, Bruce E. Pollock, M.D., a Mayo neurosurgeon says, "Unlike all linear accelerator–based radiosurgery in which the radiation source moves around the patient, with Gamma Knife radiosurgery, the patient moves relative to the radiation source. This design feature remains the same in the Perfexion, but the new model automates patient position adjustments, saving time and reducing the chance of human error. In addition, because the unit itself is larger, we are able to treat a wider range of head and neck disorders."

His neurosurgical colleague, Michael J. Link, M.D., adds, "Gamma Knife has been a great tool for neurosurgery and neuroscience at Mayo Clinic. The new model will expand our practice to include paragangliomas (glomus tumors), more meningiomas and schwannomas, and tumors of the skull base and spine. It will allow us to increase the number of patients treated for brain metastases." The new model uses a robotic system to improve the reach of the radiation beams without repositioning the headframe, changing helmets, and performing additional imaging studies. "It gives us more freedom to treat lesions on the periphery of the brain or skull base and to treat multiple tumors without the need to reapply the headframe and reimage the patient," explains Dr Link.

Radiosurgery – Fast-Growing Specialty

Radiosurgery is the fastest growing neurosurgical subspecialty at Mayo Clinic, with the majority of cases presenting with brain metastases. For benign tumors such as vestibular schwannomas (acoustic neuromas), meningiomas, and pituitary adenomas, tumor control is achieved in more than 95% of treated patients. Since the inception of the program in 1990, Mayo Clinic has maintained a continuous database of all the patients having radiosurgery, including patient characteristics, radiosurgical dosimetry, and outcomes. As Dr Pollock notes, "We are proud to have contributed to the science and practice of radiosurgery over the past 2 decades. The database has been an important addition to the practice of not only neurosurgery, but also radiation oncology. At Mayo Clinic, we value the shared expertise and interdisciplinary integration."

Cooperation extends throughout the team. As Dr Pollock says, "Our nurses work like patient caseworkers, each one assigned to a given patient. Our nurses are enthusiastic and experts in keeping patients comfortable. The colorful notes of thanks from patients on the corkboard in the waiting area are not in the database but are a valued testament to the care patients receive."

The entire team is looking forward to the new equipment—to improved patient comfort, shorter treatment sessions, and the opportunity to offer treatment to patients with conditions not previously addressed by radiosurgery.