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Department of Radiation Oncology
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About the MR-Linac Elekta Unity

What is the MR-Linac Elekta Unity?

This technology is the first machine in the world to combine a radiation delivery unit (a linear accelerator) with an MRI (high-resolution magnetic resonance imaging).

That means a patient can receive radiation treatment to a tumour while the healthcare team sees and monitors the tumour’s response in real time via the MRI. The MRI also allows us to target the tumour with fine precision, sparing surrounding healthy tissue.

How is that different than what is currently done for radiation treatment?

Typically patients receive an MRI a few days before their radiation treatment, or not at all, as MRI has traditionally been used for selected cancers (brain, head and neck, rectum). The doctors then use that MRI (and a CT Scan) to plan the radiation treatment.

Once treatment has started on a traditional radiation delivery device (linear accelerator), the patient’s position is checked using a CT before the beam is turned on. That CT does not image the tumour itself, as the CT scanner on the linear accelerator is limited (cone-beam CT) and looks only at bone to ensure daily proper patient positioning.

After radiation treatment is done (usually about 2 to 3 months later) a scan is done to see if the cancer responded.

With the combined MR-Linac technology, the ability for many more patients to have an MRI for planning is a reality. The incorporation of MRI into mainstream radiation oncology is a major advancement as the tumour (in selected cancers) can be better visualized as compared to CT.

With the MR-Linac, each day the position of the tumour itself is checked with the MRI to ensure we are hitting the target on that day. Response is also observed each day. Again this is an improvement in our current practice. If we observe a change —the tumour responding and shrinking or getting bigger due to radiation inflammation — we can make real-time adjustments based on the cancer shape itself.

This is a major step forward to personalizing radiation delivery. Using MRI in cancer radiation is not easy, and requires still a lot of work and development, which is well underway at the Odette Cancer Centre.

How was this developed?

The initial concept and research & development was performed by the University Medical Center Utrecht in the Netherlands, and together with the industry partner, Elekta AB, the MR-Linac became a prototype to commercialize.

The partnership grew to a consortium of seven founding members that represented international leaders in radiation oncology and MR imaging. For several years, the consortium worked diligently to get the prototype to the clinic. This group of founding members of the MR Linac consortium has now expanded globally to include many cancers centres.

The founding consortium members:

  • Sunnybrook Health Sciences Centre (Toronto, CA)
  • Christie NHS Foundation Trust (Manchester, U.K.)
  • University Medical Center Utrecht (Utrecht, Netherlands)
  • University of Texas MD Anderson Cancer Center (Houston, U.S.)
  • Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital (Amsterdam, Netherlands)
  • Froedtert & Medical College of Wisconsin Cancer Center (Milwaukee, U.S.)
  • The Institute of Cancer Research/ Royal Marsden NHS Foundation Trust (London, U.K.)

How does the radiation work without magnet interference?

Initially there were concerns with shooting a beam within a magnetic field, as it had never been done before and the worry was that the radiation could cause unintended damage on the surface of patients or where there is natural air in the body (like in the sinus or in the bowel). As computer software became more powerful, these effects were accounted for and patients are being treated safely thus far.

There are many challenges to working in an MR environment with respect to patient and staff safety. We have assembled and trained a team of radiation therapists that are not only certified to run a linear accelerator, but are also able to run an MRI. This team together ensures patient safety during delivery.

How is this different than stereotactic radiosurgery?

Stereotactic radiosurgery is a precise radiation technique for brain tumours and body tumours where high doses of radiation are delivered typically in 1 to 5 treatments. It has been based on MRI for tumour localization but real-time MRI monitoring has not been possible.

The MR Linac is currently being evaluated in patients that get daily delivery over several weeks. When we are confident and have the workflow established, we will transition to delivering MR-Linac-based stereotactic radiosurgery for tumours like prostate, pancreas and lymph nodes in the body where motion is an issue, unlike the brain, which is relatively fixed. It has already started at some centres globally and the pace of adoption is quickly evolving. For some indications like brain metastases and small benign tumours in the brain, the Gamma Knife Icon is a more favoured technology as the technical attributes are better served for these tumours as opposed to the MR-Linac.

Who is this machine for? Can everyone get treated on it?

In Canada, this machine is still in the research phase meaning that at Sunnybrook all patients are treated on clinical trial. Clinical trials involving patients are being run on this machine to compare it to the current standard of care, and to collect data in order to ensure the machine is being used to its maximum benefit. Only patients enrolled in a trial will be treated on this device.

MOMENTUM is the first trial on the MR-Linac, and Sunnybrook is one of seven sites participating. Doctors and the research team will invite patients to join this trial based on indications that they believe are well-suited to this technology. Sunnybrook’s trial will initially focus mainly on prostate and brain cancers.

As new MR-Linac trials begin at Sunnybrook, they will be added here

What are the side effects or risks?

Side effects are based on the cancer site that is being treated.

There may be unintended side effects due to delivering radiation in a magnetic field, and that is why this device remains in the clinical trial phase, while we investigate patient response to treatment.

What cancer is this treatment for?

At Sunnybrook, we have started to treat brain tumours with the MR-Linac, and a systematic roll out over the next year to treat prostate cancers, head and neck cancers, pancreas and other gastrointestinal cancers. These cancer types are being treated around the world by other sites with the MR-Linac, with each centre building on their experience to increase the breadth of indications.

Why can’t everyone be treated on this?

Routine radiation on advanced radiation units remains an excellent and precise treatment option for most patients. Not all cancer sites require MRI for planning or delivery.

Drawing upon our knowledge and experience, the consortium members have sorted through the cancer types that we think would be most well-suited to this new machine. These include brain tumours, prostate cancer, pancreatic cancer and rectal cancer. Now, we are investigating how to deliver the radiation using the MR-Linac as well as how to monitor response using the MRI.

Lung cancer is an example where we would not use the MR-Linac yet, as lots of research needs to be done to understand the effects of air and radiation delivery in the magnetic field. Also, research into how to image the lung with MRI is needed, as it is largely unknown and is an exciting area of potential progress.

Why does only Sunnybrook have one?

At Sunnybrook, we are committed to inventing the future of healthcare. That’s why we joined the Elekta MR-Linac Consortium many years ago. We believed – and still believe – that the future of radiotherapy lies in MRI and the ability to track tumours and personalize each patient’s radiation delivery everyday.

In our opinion, the MR-Linac was ideal technology to realize this vision.

With the leading role that Sunnybrook Research Institute has in MRI research, we have made significant progress in using the MR-Linac, and built several grant-funded programs around the central theme of MR-Guided Radiation Therapy. As a result of all our efforts, our department is ready to use this technology in the clinic and we are now treating patients in the Momentum Trial.

We know there are very hard to treat cancers in the body, and technology like the MR-Linac can result in better and more efficient radiation delivery with the aim to reduce toxicities and increase tumour cure.

How long before this is more widely used?

At Sunnybrook, we have started to treat brain tumours with the MR-Linac, and will undertake a systematic roll out over the next year to treat prostate cancers, head and neck cancers, pancreas and other gastrointestinal cancers. These cancer types are already being treated globally, with each centre building on their experience to increase the breadth of indications and exchange information to establish best practise for this new machine.

I want to learn more or get involved in a clinical trial. What do I do?

If your oncologist thinks an MR-Linac trial could be right for you, please have your oncologist complete this referral to Sunnybrook’s Odette Cancer Centre for consideration for the trial.