Experimental MR-integrated Proton Therapy
Group leader: Prof. Dr. Aswin Hoffmann
MR-integrated proton therapy: Treat what you see and see what you treat
Magnetic resonance imaging (MRI) offers real-time image guidance with unparalleled soft-tissue contrast and absence of radiation dose. The targeting accuracy of proton therapy (PT) is expected to greatly benefit from the integration of PT with real-time MRI, especially for moving tumours in the thorax, pelvis and abdomen.
The group is pioneering the following technological challenges to develop prototype systems for MR-integrated proton therapy (MRiPT) and implement this technique for first clinical evaluation:
1. Prototype development and magnetic interaction
In 2018, the group has realized the world’s first in-beam MR scanner by combining a compact, low-field, open MR scanner with a horizontal proton research beam line. In 2023, a unique whole-body, mid-field, bi-directional MR scanner capable of real-time imaging and automated tumour tracking has been installed at the horizontal proton pencil beam scanning research beam line. This system is currently being commissioned and first concurrent imaging and irradiation experiments are underway.
2. Treatment planning in presence of the MR magnetic field
For accurate proton dose calculation in the presence of MR magnetic fields, the impact of the Lorentz force needs to be taken into account. A first commercially available Monte Carlo-based treatment planning system is currently being tested and experimentally validated for this purpose. Strategies to compensate for the influence of the MR magnetic field are implemented to evaluate treatment plan quality for clinical application.
3. Dosimetric characterization, quality assurance and magnetic suitability of dose detectors
For absolute and relative dosimetry in the presence of the MR magnetic field, the magnetic suitability of dosimeters and dose detectors is experimentally determined. Phantoms and measurement concepts are developed that can be used to measure and characterize proton dose distributions in the in-beam MR scanner. Quality assurance methods tailored to the requirements of MRiPT are developed in close collaboration with the medical physics experts from the clinic.
4. On-line adaptive treatment planning
Different clinical indications are investigated to determine the dosimetric benefit of MRiPT delivered with a horizontal beamline. The benefit of adaptive treatment planning, including the impact of the magnetic field, is investigated for moving target volumes such as liver, pancreas and kidney. The dosimetric impact of breathing motion is investigated based on real-time MRI data.
5. Real-time MRI for beam gating
Real-time MRI offers the opportunity to synchronize dose application with target volume tracking during irradiation and thereby increase the targeting accuracy and reduce normal tissue side-effects. Our most recent MRiPT prototype allows for the acquisition of real-time MR images of moving target volumes during irradiation. This project focusses on the synchronization of this motion information with the proton beam delivery system and the investigation of the electromagnetic interaction between real-time MRI and proton dose delivery.
6. Proton beam visualization and range verification
In this project methods to use in-beam MRI to generate local proton beam-induced MR image contrast that is indicative of the deposited dose distribution are developed. Beam energy- and current-dependent MRI signatures resembling the associated proton pencil beam dose distribution in position and shape have been detected in experiments in liquids and motion-restricted phantoms. These methods may therefore find application in quality assurance of MRiPT.
Horizontal proton pencil beam scanning research beam line (left) with in-beam MRI system (right).
Source: © UKD/Kirsten Lassig
In-beam MRI system with vertically oriented magnet poles and horizontal patient couch.
Source: © UKD/Kirsten Lassig