Combining radiation treatments with specialized MRI proven to save healthy brain tissue

Researchers at Sunnybrook Health Sciences Centre and the University of Toronto have shown that an adaptive radiotherapy technique they developed using real-time magnetic resonance imaging not only allows for a smaller area of a brain tumour site to be targeted more precisely — therefore reducing toxicity of the radiation — but it does so while maintaining the same tumour-destroying effectiveness.

The research, part of the phase II UNITED clinical trial and published in The Lancet Oncology, is a world first. Using a specialized Elekta MR-Linac radiation system for patients with glioblastoma, the researchers beamed radiation through the skull and brain to hit the cancer, using the MRI component of the machine in real time to more accurately direct the beams, and on average reduced the amount of brain tissue exposed to radiation by 40 per cent, as compared to current standard practice.

“While this more targeted approach minimizes damage to surrounding healthy brain tissue, the question was whether the tumour grow back earlier when we target the radiation using a much smaller margin,” said Jay Detsky, principal investigator of the study, a radiation oncologist at Sunnybrook’s Odette Cancer Centre and a professor of radiation oncology at U of T’s Temerty Faculty of Medicine.

“Our goal was to not only minimize side effects by sparing surrounding healthy areas of the brain, but to show that this new high-precision approach developed at Sunnybrook still successfully treats these tumours through the use of state-of-art MRI-guidance,” Detsky said.

The standard of care puts a much larger safety margin around the tumour site to ensure it is adequately treated because these tumours can grow or shift location throughout treatment. The MR-guided radiation approach allows for a much smaller and targeted safety margin.

“By reducing the area of radiation in the brain to a five-millimetre region around the tumour site, we were able to treat tumours just as effectively as with a larger safety margin, and with less of the toxicity and side effects to surrounding healthy brain tissue,” added Detsky.

“We can do this safely because we’re adapting to the tumour as it changes throughout the six weeks of treatment and we can only achieve this because of daily MRI guidance on the MR-Linac machine.”

Research participants in the trial had to have had either a biopsy or surgical removal of a glioblastoma.

While the MR-Linac radiation system is approved for clinical treatment of patients — and used to treat a wide range of cancers including pancreatic, prostate, and breast cancers — its availability is limited and reserved for patients that would benefit the most. Sunnybrook researchers are showing its utility for glioblastoma which expands the indications for this new technology.

“When working with incurable cancers, our goal in radiation oncology is always to maximize the benefits of treatment while minimizing its side effects, and in this case, this translates to targeting and destroying as much of the cancer as possible — to slow down re-growth and prolong survival — while minimizing the amount of radiation exposure, or toxicity, to the healthy brain,” said Arjun Sahgal, senior author of the study, and chief of radiation oncology at Sunnybrook’s Odette Cancer Centre.

“These findings establish the importance of access to MR-guided radiation machines to enable this level of precision medicine that otherwise cannot be achieved with traditional radiation machines that are currently the standard of care in clinical practice.”

Sunnybrook recently received a $41-million gift to support clinical trial infrastructure, capacity and expertise. The philanthropic investment will help deliver promising therapies to more patients, faster.