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Stereotactic Radiosurgery

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New Stereotactic Radiosurgery Approach Provides Greater Efficiency, Improved Patient Experience


 Dr. Zac Labby sets up a precision measurement device before delivering a simulated SRS plan to an anthropomorphic phantom.

For many years, the Radiation Oncology Clinic at UW Hospital has had the expertise and equipment to provide state of the art stereotactic radiosurgery (SRS)—a single, high dose of radiation to treat small primary or metastatic brain tumors and other intracranial conditions.

Now, after months of preparation led by Dr. Zac Labby, assistant professor in the Department of Human Oncology at the University of Wisconsin School of Medicine and Public Health, the clinic has implemented an updated approach to SRS that combines precision, greater efficiency and an improved patient experience.

Precision and efficiency

SRS, like other radiotherapy, works by damaging the DNA of targeted cells, which causes them to lose the ability to reproduce. The difference between standard radiotherapy and SRS is the dose. SRS uses a single high dose of radiation rather than a fractionated dose administered over multiple sessions.

When delivering a high single dose of radiation to the brain, precision is essential in order to minimize damage to healthy normal tissue. Until recently, UW clinicians connected patients to a large floor stand using a frame docked directly to their head to ensure precise alignment. The technique provided excellent precision, but it was challenging and time consuming to set up.

The former SRS technique primarily delivered dose profiles that were more or less spherical. Treatment of non-spherical tumors entailed delivery of multiple spherical distributions, or isocenters, each requiring its own plan, set up and delivery.

The new system uses the clinic’s Varian TrueBeam STx machine, which features a high-definition multi-leaf collimator that enables the radiation beams to conform to the shape of the tumor as the machine rotates around the patient, providing improved dose distributions.

Instead of delivering treatment one sphere at a time—which can mean a long time on the treatment table for patients with irregularly shaped tumors—the entire tumor can be treated with just one set up.

“We can treat a very complex volume and get it all in one set of arcs,” says Dr. Steven Howard, associate professor of human oncology and brain tumor expert who directs the majority of the clinic’s SRS cases. “What used to take two or three hours, now takes a half hour. That is a huge benefit for our patients.”

For pediatric patients, reduced treatment time means less time under anesthesia, which is often needed because being immobilized during treatment is particularly challenging for children.

Highly coordinated treatment

SRS is a complex procedure that requires the coordination of a diverse team of professionals—nursing, anesthesia, neurosurgery, radiation oncology, medical physics and radiation therapy technologists.

On the day of treatment, the patient typically arrives at 7 a.m. and is prepped by a nurse for treatment, who administers conscious sedation before a neurosurgeon attaches a head frame to stabilize the patient’s head during imaging and treatment.

After the head frame is in place, the patient undergoes a fresh CT scan to identify the exact size and location of the tumor that is used for treatment planning.

“With the new system, not only will patient treatments be quicker, but we can complete the treatment planning process faster as well,” Labby says.

Treatment plans under the new system tend not to require as many modifications. This reduces a source of potential delays in treatment, says Lori Hayes, senior clinical nurse specialist, who coordinates treatment of patients who undergo SRS.

Because treatment of each tumor involves a single set up, the duration of each treatment is more predictable. A complex SRS plan with multiple isocenters that needed modifications sometimes disrupted the schedule, extending treatment well into the evening. This scenario is unlikely with the new system.

“Now, even for the most complex cases with four or five separate tumors at once, we are likely to get done in one-and-a-half hours. Many cases are done in less than 30 minutes,” Hayes says. “It really helps from a staffing perspective. With shorter treatment times and fewer delays, patients know in advance how long the procedure will take and what time they’ll be able to go home. This is a welcome improvement for patients and their families.”