Improved polymer gels for radiation dosimetry by MRI

改进的聚合物凝胶用于 MRI 辐射剂量测定

• 批准号: 6435756
• 负责人: JOHN C GORE
• 金额: $ 13.17万
• 依托单位: YALE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-15 至 2002-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6435756
• 关键词: acidity /alkalinity; bioengineering /biomedical engineering; bioimaging /biomedical imaging; biomaterial development /preparation; biotechnology; gel; magnetic resonance imaging; magnetism; molecular weight; nuclear magnetic resonance spectroscopy; polymers; radiation dosage; radiation sensitivity; temperature; xenon

The studies proposed aim to develop improved polymer gels that may be used for accurate measurements of radiation dose distributions in three dimensions. Polymer gel dosimeters were first developed in our laboratory for use with MRI, which records the changes in NMR relaxation times of water protons produced by irradiation of mixtures of monomers in an aqueous gel. Such gels are tissue equivalent and provide unique and accurate measurements of integrated dose distributions in three dimensions with high spatial resolution. Nonetheless, there remain significant problems in the use of currently available polymer gels in practice that have limited their wider use. These include difficulties of preparation and storage of gels, which must be made and kept hypoxic until used and which therefore cannot be poured in plastic or arbitrary containers: their variable sensitivity, which largely arises from the influence of trace amounts of oxygen which inhibit their response: and the limited dose response, which is based on measuring changes in T2 values that are subject to errors. The studies proposed would lead to significantly improved gels that are more sensitive, more stable, and which can be made in a normal atmosphere and any container by a hospital physicist without special procedures. In preliminary studies we have produced gels in room air that are much more sensitive than current gels. These use a novel initiator system based on copper ion and ascorbic acid which combines with and requires molecular oxygen to start polymerization when the gel is irradiated. We will optimize the performance of these dosimeters by exploring the effects of different concentrations and components of this system. We have also shown that relaxation in irradiated gels occurs via magnetization transfer (MT) between free water and labile protons in contact with a semi-solid pool in the polymer. We will design and verify the performance of MT-sensitive sequences that avoid the pitfalls of T2 measurements for imaging gels to extract accurate dose information. We also postulate that the dose- response of polymer gels simply reflects a linear increase in the size of this semi-solid proton pool with increasing dose and we will perform novel NMR and other physical measurements to verify this model. Overall we aim to produce much improved gels for practical applications and obtain a better and more quantitative understanding of how they respond to radiation.

提出的研究旨在开发改进的聚合物凝胶，可用于精确测量三维辐射剂量分布。 我们的实验室首先开发了聚合物凝胶剂量计，用于 MRI，记录水凝胶中单体混合物辐照产生的水质子的 NMR 弛豫时间的变化。 这种凝胶是组织等效的，并以高空间分辨率提供三维整合剂量分布的独特且准确的测量。 尽管如此，目前可用的聚合物凝胶在实践中的使用仍然存在严重问题，限制了其更广泛的使用。 其中包括制备和储存凝胶的困难，凝胶在使用前必须制造并保持低氧状态，因此不能倒入塑料或任意容器中：它们的可变灵敏度，这很大程度上是由于抑制其反应的微量氧气的影响而产生的；以及有限的剂量反应，这是基于测量容易产生误差的T2值的变化。 拟议的研究将显着改进凝胶，使其更灵敏、更稳定，并且可以由医院物理学家在正常气氛和任何容器中制备，无需特殊程序。 在初步研究中，我们在室内空气中制备了凝胶，其比现有凝胶更敏感。 它们使用基于铜离子和抗坏血酸的新型引发剂系统，当凝胶受到辐射时，该系统与分子氧结合并需要分子氧来启动聚合。 我们将通过探索该系统不同浓度和组件的影响来优化这些剂量计的性能。 我们还表明，辐照凝胶中的弛豫是通过自由水和与聚合物中的半固体池接触的不稳定质子之间的磁化转移（MT）发生的。 我们将设计并验证 MT 敏感序列的性能，避免成像凝胶 T2 测量的陷阱，以提取准确的剂量信息。 我们还假设聚合物凝胶的剂量响应简单地反映了该半固体质子池的尺寸随着剂量的增加而线性增加，我们将进行新的核磁共振和其他物理测量来验证该模型。 总体而言，我们的目标是为实际应用生产大大改进的凝胶，并更好、更定量地了解它们对辐射的反应。