Magnetic resonance imaging guided proton therapy (MAGIG-PRO)

The importance of magnetic resonance imaging (MRI), as a non-invasive imaging method, increased over the last years. Besides the initial applications in diagnostics, MRI nowadays also begins to enter other fields, such as radiation oncology. Image guided radiotherapy (IGRT) is based on the verification of the patients position and the actual anatomy, compared to the conditions at the day of treatment planning. Most imaging modalities in IGRT are X-ray based, which has limited soft-tissue contrast compared to MRI, and implies an additional dose burden for the patient. The improved contrast of MRI in the absence of additional dose led to recent developments for MRI guided radiotherapy. However, clinical applied solutions are focusing on radiotherapy with photons only. Particle therapy, with either protons or carbon ions, is an alternative to photon therapy. Particles are superior to photons due to their physical and biological characteristics and call for the most advanced imaging options for IGRT. The combination of MRI and particle therapy is a completely new research area, where many questions have to be investigated in detail. In principle the charged particles are deflected in the magnetic field that is used for MR imaging. This effect has to be considered already during treatment planning. The MAGIG-PRO project will investigate different magnetic field strengths to establish new models for proton dose calculations in magnetic fields. Furthermore, the usage of MR images for dose calculation would have advantages over the usage of computed tomography (CT) images. This procedure can increase the accuracy of dose calculation and henceforth the treatment quality. However, there are very limited studies dealing with this issue. Thus, methods and algorithms will be developed to derive the atomic stopping power directly from MR images in the framework of MAGIG-PRO. In Austria particle therapy will be available with the end of 2016 at the MedAustron center in Wiener Neustadt. Experiments under realistic clinical conditions will be conducted using a dedicated magnet in the research room at MedAustron. Beforehand computer based simulations will be performed to enable a detailed preparation of the complex experimental setups. The MAGIG-PRO project includes several new research aspects, which go beyond the proof of principle of MRI guided proton therapy. The cooperation between the Medical University of Vienna and MedAustron enables unique experimental conditions for this project. The research outcome of the MAGIG-PRO project will position the research team in the forefront with respect to MRI guided proton therapy.

The FWF stand-alone project MAGnetic resonance Imaging (MRI) Guided PROton therapy ("MAGIC-PRO") aimed at basic medical radiation physics and technology oriented research in order to combine the most precise imaging technology, i.e. magnetic resonance (MR) imaging, with the most precise dose delivery technique, i.e. proton therapy. The concept of MR guided proton therapy defines a new and unprecedented level of image guidance in radiation oncology. The principal objectives of the MAGIC-PRO project were twofold. First, to develop methodologies and algorithms for proton dose calculation on synthetic computed tomography (CT) images generated from MRI. For the generation of synthetic CTs, which include density information and are thus needed for dose calculation, the focus was given to artificial intelligence (AI) based solutions. Second, to develop an analytical dose calculation algorithm for treatment planning and/or treatment plan optimization for proton therapy in the presence of a magnetic field. These developments focused on a sophisticated pencil beam model. In overall context of the MAGIC-PRO, research was performed in the field of experimental proton dosimetry in the presence of magnetic fields. This aspect was important for the validation of the inhouse developed dose calculation algorithm. Next, a complete patient workflow was tested for proton therapy including MR image acquisition, imaging conversion and dosimetric analysis of MR based treatment planning. This workflow demonstrated the feasibility of using an open low field strength MR scanner for MR guided proton therapy. MR guided proton therapy was in its infancy when the MAGIC-PRO project was initiated in 2017. Since then, the topic has stimulated research in leading European centers. Thanks to the FWF funding and the available infrastructure including a research magnet at the Austrian ion beam facility MedAustron, significant contributions could be made by the two PhD students hired via the project in the following fields: (1) Generation of synthetic CT (sCT) from MR images including QA, (2) Proton dose calculation and treatment planning in magnetic fields, as well as (3) Experimental proton dosimetry in magnetic fields. The promising results and achievements generated via the MAGIC-PRO project have increased the visibility of ion beam research in Austria. Based on the in-house development and expertise built up during this project, researchers of the Medical University of Vienna have been invited to participate in an international cooperation on MR guided proton therapy.