These live images help keep the radiation beam directly on target throughout every treatment, allowing for a degree of precision and monitoring capabilities that were not previously possible.
Marriage of two technologies
The technology, known as the MR-linac, merges a high-strength magnetic resonance imaging (MRI) machine and a linear accelerator into a single device. The MRI machine provides high-quality, real-time images of tumors as they’re blasted with radiation beams from the linear accelerator.
MRI machines and linear accelerators have been used separately in the care of cancer patients for years. High-field, diagnostic-quality MRI provides good visualization of the tumor and the surrounding tissues and allows evaluation of response to treatments. Linear accelerators have advanced to deliver high-precision radiation treatment to the tumor. Until recently, extra imaging meant additional radiation dose, and imaging. However, the integration of these two powerful technologies into one machine allows radiation oncologists to track and monitor the movement of tumors during radiation delivery, and potentially track radiation response in real-time, without any added radiation dose to the patient.
Changing the radiation treatment game
Before the MR-linac’s debut, scientists wouldn’t dare place a 1.5 Tesla diagnostic MRI machine near a linear accelerator.
There were many technical challenges to integrating a high-field MRI with a linear accelerator, requiring either lower field strength or the use of radioactive sources to deliver therapy and imaging without the interference of one component with another. The MR-linac’s developers, led by Jan Lagendijk, Ph.D., at the University of Utrecht, The Netherlands, created a simple but elegant workaround: splitting the MRI in half to create a space in the magnetic field, and placing the accelerator in the “gap”. This allows radiation to pass through the “gap” and images to be created without distortion.
Improved tracking with better visibility of the tumor
“When patients breathe in and out, tumors can shift in position by an inch or more,” explains Clifton David Fuller, M.D., Ph.D., associate professor of Radiation Oncology. “This movement has in the past made it difficult for us to pinpoint a tumor’s exact location during radiation delivery.”
Doctors used to treat the entire area where the tumor might travel during a normal breathing cycle.
“With real-time monitoring, we can now see, and soon track, that tumor motion,” Fuller says.
While tracking itself is not new, the ability to track the tumor with improved diagnostic quality resolution is a major improvement over existing radiation delivery systems.
Likewise, the MR-linac allows soft tissue and tumors to be monitored from one daily treatment to the next, and modified if a change occurs. Since MRI does a better job at showing soft tissues than X-rays or other imaging, this is a large improvement, minimizing the chance of radiating the healthy organs near the tumor.
“Because the risk of collateral damage is reduced, even when delivering the same radiation doses, treatment is made safer because we can now see the target and the normal anatomy we are trying to spare more accurately,” Fuller notes.
Collaboration leads to approval for patients in Europe and the US
In 2012, MR-linac manufacturer Elekta and its technology partner Philips formed the MR-linac Consortium — an international research collaboration set up to study image-guided radiotherapy and help facilitate evidence-based introduction of the technology. Joining the original development team in Utrecht, MD Anderson helped lead the way in developing the innovative technology as a founding member of the consortium, which began with seven member institutions in the U.S., Canada and Europe, and today consists of more than 300 scientists at 12 institutions. MD Anderson has been an active participant and provided substantive support to the international consortium, serving as a development and implementation site, all of which were essential to the MR-linac gaining approval by the U.S. Food and Drug Administration (FDA).
The MR-linac received the CE mark in June 2018, allowing its clinical implementation in Europe. That was followed by FDA approval in December 2018. This month, MD Anderson became one of the first hospitals in North America to treat a patient using the MR-linac. The institution was also one of the first clinical sites in the world to install the device.
A team effort to move radiation therapy forward
Implementing such a new technology required years of development across member sites of the international consortium.
Jihong Wang, Ph.D., a professor of Radiation Physics, oversaw the technical aspects of the project such as equipment installation and operation, calculating radiation dosages, and ensuring safety precautions were in place. It took a collaborative effort from a team of physicists, radiation therapists, IT specialists, dosimetrists, safety officials, operations staff and administrators, as well as facilities and machine teams, to install and calibrate a multi-ton device with millimeter precision.
That same team is now working to define even more innovative approaches to using real-time imaging. The new technology has the potential to enable substantial leaps in personalized image-guided radiation therapy to greatly improve care and outcomes for many.
“Half of all cancer patients undergo radiation treatment,” Fuller says. “All could potentially benefit from this game-changing technology.”
The MR-linac merges a high-strength magnetic resonance imaging (MRI) machine and a linear accelerator into a single device. The name reflects the merger of the two technologies: MR, for magnetic resonance, and linac, for linear accelerator. photo by Nick de la Torre