Dosimetry in magnetic fields for MR-guided ion therapy

Ion beam therapy offers enhanced dose distribution and biological effectiveness compared to traditional photon radiation therapy. However, its potential has been partially constrained by the lack of sophisticated image guidance during the treatment process. The integration of Magnetic Resonance (MR) imaging with ion beam therapy could represent a paradigm shift allowing real-time adaptive strategies to account for both inter- and intra-fractional anatomical changes with the highest soft-tissue contrast. Nevertheless, its clinical implementation necessitates accurate dosimetry in the presence of magnetic fields. One of the associated primary challenges is the interaction between the primary ion beams, as well as the secondary charged particles, and the applied magnetic field. This interaction can significantly alter the dose distribution, beam quality, the LET distributions, and potentially the biological effectiveness. Additionally, the alteration of particle fluence may lead to perturbations of detector response based on the beam quality or detector orientation. The proposed DosiMagic project aims to provide a dosimetry solution as an essential milestone to enable the clinical realization of MR-guided ion beam therapy. The overall goal is to extend dosimetry in particle therapy towards magnetic field environment by developing guidelines for good clinical practice for proton and ion beam dosimetry in magnetic fields. Three objectives are laid out to achieve this goal: 1. Investigation of general effects of magnetic fields on the beam quality in particle beams; 2. Establishing correction factors for reference and non-reference dosimetry in magnetic fields; and 3. Translation to best practice particle therapy dosimetry in magnetic fields. These objectives are built on the outcome of the work packages comprising the thorough theoretical understanding of the effect of magnetic fields on the beam properties as well as the experimental and Monte Carlo investigations of detectors behaviors under reference and non-reference (relative) conditions. The research project is to be carried out as cooperation between 5 research institutions in Germany and Austria. Each of the participating research groups contributes to the project with expertise covering experimental design and execution, Monte Carlo modeling and simulations, clinical know-how and experience in dosimetry guideline development. This setting offers a unique combination of expertise to carry out the work packages carefully designed according to the employed methods to fully utilize the know-hows of the leading institutions in each work package. The final outcomes of our project, including the establishment of clinical guidelines and protocols providing the detectors correction factors, will support the implementation of MR-guided ion therapy that holds promises for increased precision of dose delivery, reduce side effects, and improve overall treatment outcomes.