Ambition

The Unity 1.5T MR-linac was clinically introduced to achieve stereotactic accuracy for tracking moving targets. We set out to test whether combining the MR-linac with PET/MRI could enable PET data to guide stereotactic radiation therapy, and built a dedicated prototype system to explore exactly that.

Vision

The prototype was designed to sit in a treatment pipeline together with the MR-linac. The availability of MR images allowed a precise transfer of PET/MRI information to the MR-linac system for treatment guidance, making pathophysiological information available for real-time guidance on the MR-linac. The main purpose of the pipeline was to localize and characterize the pathophysiology of metastases through motion compensation — working toward more precise radiation, reduced toxicity, and better patient outcomes.

Design

The design of the prototype facilitated this vision. The system offered a 70 cm bore size and PET detectors mounted in the gap of a split gradient coil. Its MRI hardware was largely shared with our MR-linac system: both used a 1.5T magnet and identical hardware such as the gradient coil, body coil and amplifiers. This shared hardware resulted in near-identical image quality and patient positioning between the two systems, enabling a spatially accurate transfer of pathophysiological information from the PET/MRI prototype to the MR-linac. Both systems were built explicitly to track patient motion and adapt treatment accordingly.

Partners

Realizing the prototype was very much a team effort — a nice showcase of what a multidisciplinary academic-industry consortium can build together:

• Uniklinik RWTH Aachen (DE)
• Philips Healthcare (NL)
• Futura Composites (NL)
• UMC Utrecht (NL)
• Hyperion Hybrid Imaging Systems (NL)