MAGNETIC RESONANCE GUIDED ENHANCED RADIOTHERAPY

拟议的研究将整合最先进的线性加速器和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能够在显示电离粒子辐射束（如电子、质子、重离子）路径的同时，对转体和周围组织进行成像。该研究将在同一物理空间内创造一种将放射治疗与诊断成像相结合的新方法，具有高度的创新性。组织的核磁共振弛豫特性将改变在一个强烈的粒子电离辐射束的存在。发生这种情况的原因如下：(1)电离辐射，如电子束、p+束等，在它们通过的物质中产生带电粒子。在水系统中，自由基在电离辐射下形成。这会产生沿辐射路径的磁化率差异，从而影响区域磁场的均匀性。T2（即由于磁场不均匀性引起的自旋-自旋表观弛豫）应受到影响并可测量；(2)来自自由基的未配对电子，尤其是水合电子，与水的相邻质子自旋相互作用，降低了T1（自旋-晶格）和T2（自旋-自旋）弛豫时间；(3)电子束会造成局部磁场的微小扰动，导致核磁共振信号的相移或相相干性的丧失。通过获得T1， T2和T2*加权MR图像，可以可视化放射治疗期间的放射束。这样可以准确地测定肿瘤和健康组织的原位辐射剂量。没有一种形态能做到这一点。辐射场的实时成像为在器官移位存在问题的身体区域进行动态肿瘤靶向开辟了道路。

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.