What’s New for Image-Guided Radiotherapy?

What’s New for Image-Guided Radiotherapy?

Every so often a new therapy shifts the landscape of current practice. It’s a game changer – a disruptive technology. For the past two decades the use of image-guided radiotherapy, using computed tomography (CT), changed the way radiation therapy was delivered to patients with cancer. However, a new technology – magnetic resonance imaging-guided radiotherapy (MRgRT) – is emerging in Canadian practice. Will MRgRT be the game changer CT was?

Radiation therapy is a common treatment for cancer and can be used alone or in combination with chemotherapy and surgery. While CT guided radiotherapy is the current standard of care, a new technology is emerging, and in 2017 the first MRgRT system was approved by Health Canada. MRI may have an advantage over CT guided radiotherapy, as MRI can quickly image soft tissues, which may make it better for visualizing and treating areas that are susceptible to movement in the body (for example movement associated with breathing and bowel motion). Some modalities of MRgRT, such as MR-linac, combine a magnetic resonance imaging (MRI) scanner, which guides the delivery of radiation to the tumour, with a radiotherapy accelerator into one device. The combination of these technologies allows the precise delivery of radiation to the tumour site, while minimizing any potential radiation-related damage to the surrounding tissues. The goal is improved outcomes for patients and health care systems.

To learn more about MRgRT delivery systems, CADTH, which stands for the Canadian Agency for Drugs and Technologies in Health, undertook a Health Technology Update and Rapid Response report (i.e., a rapid evidence review) to see what evidence might be available regarding these technologies. The Health Technology Update, which falls under CADTH’s Horizon Scanning Service, provides brief articles on new and emerging technologies that may be relevant for Canadian health care systems. Our Rapid Response program offers timely evidence reviews to help support health care decision makers.

The Health Technology Update looked at MR-linac systems. At the time of the article (March 2019), there were three facilities in Canada conducting research with MR-linac; one facility in Edmonton, and two facilities in Toronto. The article noted the benefits of using an MR-linac system which can find and treat tumours at the same time. One of these benefits is that if a patient moves during this therapy, even due to normal internal body movement, and the tumour moves out of the field of the targeted radiation, the MR-linac can automatically stop the radiation beam until the tumour moves back into position. And while MR-linac could be used to treat almost any type of cancer, it is anticipated that MR-linac will be initially used for brain, breast, cervix, esophagus, lung, oropharynx, pancreas, prostate, and rectal cancers. However, the CADTH horizon scan also noted the high cost of MR-linac (Canadian costs aren’t known, but in the United Kingdom, installation of MR-linac cost 5.3 million pounds), which may be a barrier to using this type of technology.

It’s also anticipated that MR-linac systems will be operated by a larger team of professionals compared to CT. While CT-guided systems require radiotherapists, due to the novelty of MRI-guided therapies, they will require a team composed of physicians, radiotherapists, medical radiation technologists, and physicists.

In terms of existing research, both the Health Technology Update and Rapid Response noted the lack of research. The Rapid Response report looked for comparative clinical effectiveness (MRgRT systems compared to other image-guided hybrid systems, non-hybrid systems, or before and after treatment comparisons), cost-effectiveness studies, and evidence-based guidelines (full details and questions can be found at: https://www.cadth.ca/magnetic-resonance-imaging-guided-radiotherapy-delivery-systems-cancer-treatment-review-clinical). Only one study was found which compared MRgRT to a linear accelerator system for the treatment of patients with lung cancer. It appeared that there was no difference in lung density between the two systems; however, the study had several limitations and was of low-quality. No cost-effectiveness studies or evidence-based guidelines were found, likely due to the novelty of the therapy. The Rapid Response report concluded that the effectiveness of MRgRT for treating patients with cancer remains uncertain at this time.

What does this all mean for MRI-guided radiotherapy? And specifically, for MR-linac – a new technology, with limited availability in Canada. While it looks like it might be a promising new therapy to treat patients with cancers requiring radiation, it’s still very early days in terms of the evidence for its clinical effectiveness. Only time will tell whether this therapy will replace CT-guided radiation!

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