MAGNETIC RESONANCE GUIDED ENHANCED RADIOTHERAPY

拟议的研究将整合一个国家的最先进的直线加速器与1.5 T MRI系统，以产生第一代诊断治疗模式。 将磁共振扫描仪与放射治疗单元相结合产生协同作用，并形成磁共振引导增强放射治疗（MR-GERT）的基础。 MR-GERT具有对肿瘤和周围组织成像的能力，同时使电离微粒辐射束的路径可视化，例如，电子质子重离子 这项研究具有高度创新性，因为它将创造一种新的方法，将放射治疗与诊断成像结合在同一物理空间中。组织的NMR弛豫特性将在强粒子电离辐射束的存在下改变。 这是由于以下原因而发生的：（1）电离辐射，例如电子束、p+束等，产生带电粒子。 在含水系统中，在暴露于电离辐射期间形成自由基。 这产生了沿着辐射路径的磁化率差异，这将影响区域磁场均匀性。 T2（即由于磁场不均匀性引起的明显自旋-自旋弛豫）应受到影响并可测量;（2）来自自由基的未成对电子，特别是水合电子，与水的相邻质子自旋相互作用，将降低T1（自旋-晶格）和T2（自旋-自旋）弛豫时间;（三）电子束将产生局部磁场的小扰动，导致NMR信号的相移或相位相干性的损失。通过获得T1、T2和T2 * 加权的MR图像，可以在放射治疗期间可视化放射束。 这允许准确确定对肿瘤和健康组织的原位辐射剂量。 没有任何形式可以做到这一点。 辐射场的真实的实时成像开辟了在器官移位是问题的身体区域中动态肿瘤靶向的途径。

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.