An MRI-guided radiation therapy system is inching closer toward reality. A research group composed of Philips Healthcare, Elekta, and the University Medical Center Utrecht in the Netherlands recently announced that the University of Texas MD Anderson Cancer Center has signed on to partner in advancing an MRI-guided radiation therapy system — which is only a prototype at this point — to the next stage of development.

"The success of the prototype system at the University Medical Center Utrecht has enabled us to move to the next phase of development and testing," Christopher Busch, senior director of new business development for MR therapy at Philips Healthcare, told DOTmed News. "Since the primary purpose of that prototype was to demonstrate the technical feasibility of an MRI-guided radiation therapy system, it was not designed to meet all the specifications for clinical studies nor was it scalable for production."

This is where MD Anderson enters the picture. The prototype, which integrates Elekta's linear accelerator and Philips Ingenia 1.5 Tesla MR system, will need to be refined to meet specifications for clinical trails. From this, a limited series of pilot systems will then be produced, which will be tested by clinical researchers at MD Andersen, as well as the University Medical Center Utrecht.

"We certainly think that the MRI-guided radiation therapy technology has the potential to become a game changer in cancer care, but we still have to prove that," said Busch.

Traditionally, CT scans are used in radiation therapy treatment planning. Radiologists, medical physicists, dosimetrists and radiation therapists work with a computer generated model of the patient based on 3D CT images to identify the tumor and organs at risk.

But researchers believe that MR is poised to play an increasing role in radiation therapy because of its increased soft tissue contrast and functional imaging capabilities. MR scanning alone can give clinicians sophisticated information for staging, planning of treatment and post-treatment evaluation of numerous types of tumors, for example.

"I think this combination can emerge as an optimal form of image guided radiation therapy where we provide more precise targeting of the tumor to improve cure rates and less radiation to normal tissues resulting in a reduced toxicity of treatment," Dr. Steven Frank, director of advanced technologies for radiation oncology at MD Anderson, told DOTmed News.

Combining an MR scanner and a linear accelerator certainly presents challenges. For starters, a linear accelerator cannot operate in an MR scanner's magnetic stray field and the radiofrequency (RF) from the linear accelerator would normally prevent the MR scanner from working. There's also the issue of the radiation beam from the linear accelerator getting in the way of any coils or electronics on the MR machine and compromising imaging quality. To overcome these issues Busch said the research team has developed novel designs for the MRI magnets and gradient coils.

"This enables magnets that are similar to current commercial designs but with a transparent window for the radiation beam to pass through. We have also redesigned the magnet architecture to create a so-called toroidal zone around the scanner that has zero magnetic field, where the linear accelerator can operate," he said.

In addition, they have developed novel RF shield concepts to isolate the MR components from the linear accelerator for high performance of both components.

Since there is still a lot of work to do, Busch said testing and evaluating the approach will still be ongoing for the next several years.