MAGNETIC RESONANCE GUIDED ENHANCED RADIOTHERAPY

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The proposed research will integrate a state-of-the-art linear accelerator with a 1.5 T MRI system to yield a first generation diagnostic-therapeutic modality. Combining a magnetic resonance scanner with a radiation therapy unit yields a synergy and forms the foundation for Magnetic Resonance Guided Enhanced Radiation Therapy (MR-GERT). MR-GERT has the capability of imaging a turr and surrounding tissue while simultaneously visualizing the path of an ionizing particulate radiation beam, e.g., electron, proton, heavy ion. The proposed research is highly innovative in that it will create a new methodology that combines radiation treatment with diagnostic imaging in the same physical space. The NMR relaxation properties of tissue will alter in the presence of an intense particulate ionizing radiation beam. This occurs for the following reasons: (1) ionizing radiation such as e-beams, p+beams, etc., generate charged particles in matter through which they pass. In aqueous systems, free radicals form during exposure to ionizing radiation. This creates susceptibility differences along the radiation path that will affect regional magnetic field homogeneity. T2 (i.e. apparent spin-spin relaxation due to magnetic field non-uniformity) should be affected and measurable; (2) Unpaired electrons from free radicals, especially the hydrated electron, interact with neighboring proton spins of water and will reduce T1 (spin- lattice) and T2 (spin-spin) relaxation times; (3) The electron beam will create a small pertubation of the local magnetic field resulting in a phase shift or loss of phase coherence of the NMR signal. Visualization of a radiation beam during radiation treatment should be possible by obtaining T1, T2 and T2* weighted MR images. This allows accurate determination of radiation dose to tumor and healthy tissue in-situ. No modality exists that can do this. Real time imaging of the radiation field opens the way to dynamic tumor targeting in regions of the body where organ displacement is a problem.