MRiPT technology: prototype for new approaches in cancer treatment

MRI-integrated proton therapy (MRiPT) marks a significant advance in cancer treatment by increasing the precision of radiation treatment. In an interview with MEDICA.de, Prof. Aswin Hoffmann presents current technological challenges and highlights the potential benefits of real-time MRI imaging for proton therapy.

Prof. Hoffmann, what technological limitations do you currently see in MRI-guided proton therapy? Are there already ideas on how these could be overcome?

Prof. Aswin Hoffmann: An “MRiPT” system, in which an MRI scanner is combined with a proton irradiation system, currently only exists as a prototype, as there are still many technical challenges to overcome. With our first MRiPT prototype based on an MRI scanner with open magnetic geometry, we demonstrated for the first time worldwide in 2020 that image artifacts can occur during simultaneous proton irradiation and MR image acquisition. These impair the image quality to such an extent that the images are unusable for image-guided proton therapy. We were able to identify the cause of this: Certain components of the magnetic field generated by the proton irradiation system interfere with the magnetic field of the MRI. Magnetic shielding must be developed to ensure undisturbed image quality.

With the new real-time MRI installed at the University Proton Therapy Dresden at the beginning of 2024, it will be technically possible for the first time to perform live imaging and proton irradiation simultaneously. However, we do not yet know whether the quality of the live images will be impaired during proton irradiation. If this is the case, as with the previous prototype, we will have to rethink and develop new magnetic shielding solutions for this MRI.

What are the advantages of real-time MRI imaging compared to conventional imaging methods in proton therapy?

Hoffmann: Conventional imaging techniques in proton therapy are based on X-ray imaging, which has poor image contrast for soft tissue. The advantage of MRI over X-ray is that it provides excellent soft tissue contrast, so we can better see where we need to aim our beams to hit the tumor accurately and precisely.

In addition, real-time MRI offers the ability to image tumors that move during radiation due to respiration (lungs, esophagus, liver, kidney), heartbeat (esophagus) or organ filling (bladder) in real time to track the movement.

The aim of the project is to synchronize the application of the dose with the tumor movement. This increases the accuracy of hitting the tumor and reduces the dose delivered to the healthy tissue around the tumor. This reduces the risk of side effects.

What technical challenges had to be overcome to successfully integrate the MRI device and the proton irradiation system?

Hoffmann: First of all, an MRI had to be found that would make it possible to bring the proton beam into the MRI's field of view without the beam being influenced by components of the MRI. An MRI with an open magnet geometry proved to be the best solution.

Secondly, we had to ensure that the magnetic field of the MRI was not influenced by external magnetic fields generated by the proton irradiation system. For a static proton beam, which does not move during dose delivery, we were able to do this successfully. For a dynamic, magnetically controlled proton beam that scans the tumor during irradiation, there are still challenges in avoiding the interference from these external magnetic fields in the MRI images.

Thirdly, the magnetic field of the MRI has a direct influence on the course of the proton beam. The protons are positively charged particles that move from the irradiation system to the person in the MRI's magnetic field. This causes the proton beam to be curved. Fortunately, this effect can be calculated in advance with a high degree of accuracy and validated experimentally.

How do you assess the cost-benefit ratio of the new technology compared to conventional treatment methods?

Hoffmann: We are currently in a research and development process that is supported by funding from the Free State of Saxony, the German federal government and industry partners. The final costs for the acquisition and operation of such a novel “MRiPT” system will of course be higher than for conventional proton therapy without MRI guidance, as additional functionality has been added.

The clinical added value of this new technology must first be proven by clinical studies that show that the accuracy of proton therapy of moving tumors is increased, thus reducing the risk of side effects. The avoided side effects could save costs and the number of sessions could also be reduced and the radiation dose per session increased. The cost-benefit ratio of the technology must be demonstrated by future cost-effectiveness studies.

What long-term effects do you expect the integration of real-time MRI into proton therapy to have on patient safety and experience?

Hoffmann: In radiotherapy, patients are usually irradiated while lying down, with the radiation machine rotating around the patient to direct the beam at the tumor from different directions and thus spare surrounding healthy tissue as much as possible. As the radiation device for proton therapy must be very large (approx. 10 m in diameter), the construction and purchase of such a system is associated with high costs.

To reduce the investment costs, we want to literally reverse the existing concept: We want to rotate the affected person relative to a fixed irradiation device. This means that the patient will not be lying down but sitting or standing.

What are the next steps for the “MRiPT” technology?

Hoffmann: There are still a few technical hurdles to overcome before it is ready for use in humans. One of the most important challenges is that we don't yet know how good the MR image quality will be with simultaneous live imaging and proton irradiation.

Finally, a lot of time is still needed to meet the legal requirements of the new Medical Device Regulation (MDR). A process has already been started for this, in which we are working towards guaranteed safe use and certification of the device based on prospective risk analyses.