Trusted MR-guided radiotherapy planning

Challenge

Europe’s health services face demands for breakthrough cancer therapies assured as safe, personalised, and able to cost-effectively treat patients.

In 2020, 2.7 million people in the European Union received a cancer diagnosis. About half underwent radiotherapy, including during diagnosis. Image-guided radiation therapies became common for diagnosis and treatment, combining therapy and imaging technologies in one device. Computed tomography emerged as the dominant imaging technology but its use of multiple X-rays limits how much imaging can be used.

By contrast, MR-guided radiotherapy (MRgRT), which combines Magnetic Resonance Imaging (MRI) with high-energy photon or X-ray beams for therapy, offered zero additional radiation exposure and so unlimited imaging. The higher soft-tissue contrast of MRI also provides easier differentiation between healthy and cancer cells, and continuous imaging aids correct positioning during treatment. Combined, these advantages offered better patient outcomes and reduced side effects.

Elekta, a medical technology company and leader in precision radiation therapy, along with University Medical Center Utrecht (UMCU), Phillips and others developed an MRgRT (or MR-linac) concept, installed as the world’s first clinical prototype in 2014. The Elekta Unity was designed so clinicians could see tumours and surrounding healthy tissues as treatment doses are delivered, so can effectively be adapted for changes in patient anatomy between sessions.

Successful clinical radiotherapy depends on delivering accurate radiation doses to patients to the right area - typically supported by trusted codes of practice. However, magnetic fields, which are part of the working principle of MRI scanners, were shown to interact with treatment beams and measurement equipment. The Elekta Unity was designed to mitigate effects on the generation of the treatment beam, but the effect of magnetic fields on measurement devices used by clinicians for calibrating and characterising radiation fields as part of treatment planning was unknown, and not described in codes of practice.

Elekta developed its treatment planning software (TPS) so clinicians could calculate optimal dose distributions for each treatment session, the accuracy of which was relied on an underlying beam model and measured dose input data. While prototypes of the Unity showed the capability of accurate dose delivery, for Elekta to be confident that personalised doses could be delivered in practice, strong evidence was needed to show the reliability of its TPS.