Gamma Knife ICON: Enhancing Treatment for Brain Metastasis and Benign Tumours

THIS IS AN EXCERPT FROM THE 2017-2018 ANNUAL REPORT.

Gamma Knife Frame

Radiation oncologists and neurosurgeons have traditionally used a surgically-placed metal frame when treating brain metastases and benign tumours, such as meningiomas and vestibular schwannomas, with high single doses of radiation. The frame is part of the highly sophisticated Leksell Gamma Knife, which uses 192 small individual beams targeting the tumours in a patient’s brain. With the frame surgically attached to the patient’s skull, the patient is rigidly
immobilized on the treatment table, allowing the deposition of the high dose radiation to the tumour site.

A patient’s typical day starts out in the early morning, when the neurosurgeon attaches the frame to the patient’s head. The patient is then imaged with CT and MR scanners; the clinician designs a treatment plan based on these images, and the patient is treated later the same day.

In most other types of radiation, the full dose is usually divided into a number of smaller fractions. “The frame limits the ability to treat lesions with more than one fraction of radiation,” said Dr. David Shultz, Co-Director of the Brain Metastasis Clinic at Princess Margaret Cancer Centre. “With the Gamma Knife, we’ve always delivered single fraction radiotherapy because the frame is too uncomfortable to put on for more than one day.”

When several patients are treated on the same day, it can also be quite demanding on the clinicians. “There is a lot of pressure to do the planning and preparation on the day when the patient has the frame on,” said Dr. Hany Soliman,
Radiation Oncologist at Sunnybrook’s Odette Cancer Centre. “So it is resource intensive on that day and if something goes wrong you have to start the process over again.”

To address some of these concerns and give clinicians more treatment options, a new technology was developed to enhance the Leksell Gamma Knife called the “ICON.” The ICON technology would provide clinicians more options to
tailor cancer treatment, while maximizing patient comfort, immobilization accuracy, optimizing patient scheduling and allow multi-day treatments.

Gamma Knife ICON Development

Dr. David Jaffray, Head of the Department of Medical Physics in the Radiation Medicine Program at Princess Margaret, had been working on integrating imaging systems into radiotherapy machines. His team took a few years to design an initial prototype, then shared the idea with Elekta and patented it. Elekta adopted the new technology, and collaborated with David J. and his team to create a prototype, which was ultimately approved by Health Canada. This technology has since then been commercialized by Elekta, and the first version of the Gamma Knife ICON was released three years ago. The development of the ICON at Princess Margaret took over five years, and involved a multi-disciplinary team consisting of radiation oncologists, physicists, therapists, machinists and engineers. Some of the key players included Physicists Drs. Mark Ruschin and Young-Bin Cho, post-doctoral Fellow Dr. Greg Bootsma, Radiation Oncologists Drs. Cynthia Menard and Caroline Chung, Radiation Therapist Winnie Li, Research Associates/Engineers Philip Komljenovic and Steve Ansell, and Machinist Rod Martin.

“When we worked with the company, we stepped them through what kind of changes would be possible to apply to the machine as the patient is having treatment,” said David J. “I think this is one of the most interesting parts because you’re making adjustments while the patient is on the table and to do that safely and with confidence requires a lot of technological innovation that we contributed to make sure that it works.”

With the ICON technology, it is now possible to use a thermoplastic mask for immobilization, with the frame of reference generated through an integrated cone beam CT apparatus. These images are then registered to the planning image, through which, the machine localizes the tumour target in the brain, defined by the stereotactic coordinates from the frame.

“The CT scanner that is part of the ICON makes a kind of digital frame,” said David J. “The digital frame with great precision and accuracy tracks the machine to the skull. All the imaging information is being registered back to the skull through computers.”

There is also a threshold that the machine watches and if the patient moves beyond that threshold during treatment, the treatment will stop.

Benefits of the ICON

With the mask, clinicians can now treat patients over multiple days as opposed to only a single fraction. By integrating the imaging during treatment, different radiation courses can be explored. “For a tumour of a certain size, there is only so much radiation you can deliver in a single fraction before you are at high risk of causing injury,” said David S. “But you can give a slightly smaller dose every day, so that the cumulative dose is quite significant while minimizing the risk of injury, allowing us to improve care by fractionating treatment when appropriate.”

Although the metal frame can still be used on the ICON, clinicians now have the option to more finely tailor the most suitable type of treatment for their patients. When using the mask-based approach, patients no longer need to come in early and wait all day while wearing this heavy metal frame. The ICON technology can also improve efficiency; thereby saving cost, and increase treatment availability.

The Odette Cancer Centre started using the ICON in June 2017, primarily treating brain metastases. The majority (80%) of patients are treated with the mask; 20% still treated with the frame. “This is a big step for us,” said Hany. “It is not often that you get a machine that improves patient experience, outcomes and efficiency within a department. The number of patients that we have treated so far is a testament to the success of the ease of use of the ICON.”

The Princess Margaret also started using the ICON in 2017, although there is still a preference for using the frame to treat smaller lesions. David S. opined that, “The ICON has the ability to deliver radiation using either a mask or a frame so it can do both, but many of our patients are still treated with a frame because we prefer using it for smaller lesions.”

Currently, there are five ICON machines in Canada, including the two at Odette and the Princess Margaret. The other three are located in Quebec, Winnipeg and Alberta. Both Odette and Princess Margaret receive referrals from other cancer centres, including Southlake, Credit Valley Hospital, Royal Victoria Hospital, as well as from other sites throughout Ontario and outside the province.

Future Use

David J. describes the precision of the ICON technology and how it allows for the exploration and improvement of alternative radiation treatments in the brain. Being able to calculate doses and integrate imaging within an adaptive paradigm that also incorporates a safety system is highly advantageous. “As we move into more online image guided systems, this paradigm of integrative imaging and adaptation in the room is going to become more common,” said David J. “I think the ICON is a glimpse of what that’s going to look like in the future, and having the imaging directly integrated is very attractive from a quality assurance perspective.”

Odette Cancer Centre ICON team
Back row L to R: Lori Holden, Mark Ruschin, Arman Sarfehnia, Hany Soliman
Front row L to R: Sten Myrehaug, Brige Chugh, Young Lee, Collins Yeboah, Eric Tseng, Arjun Sahgal

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