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: 6621693
• 负责人: JOHN C GORE
• 金额: $ 17.69万
• 依托单位: VANDERBILT UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-27 至 2005-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6621693
• 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.

这些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。 聚合物凝胶剂量计首先在我们的实验室中开发用于MRI，其记录水质子的NMR弛豫时间的变化，所述水质子通过照射水凝胶中的单体混合物而产生。 这样的凝胶是组织等效的，并且提供具有高空间分辨率的三维积分剂量分布的独特且准确的测量。 尽管如此，在实践中使用目前可用的聚合物凝胶仍然存在限制其更广泛使用的重大问题。 这些包括凝胶的制备和储存的困难，其必须制备并保持低氧直到使用，因此不能倒入塑料或任意容器中;它们的可变灵敏度，这主要是由于抑制其响应的痕量氧的影响;以及有限的剂量响应，这是基于测量T2值的变化，这是有误差的。 拟议的研究将导致显着改进的凝胶，它们更敏感、更稳定，并且可以由医院物理学家在正常大气和任何容器中制备，无需特殊程序。 在初步研究中，我们已经在室内空气中产生了比目前的凝胶更敏感的凝胶。 这些使用基于铜离子和抗坏血酸的新型引发剂系统，当凝胶被照射时，该引发剂系统与分子氧结合并需要分子氧来开始聚合。 我们将通过探索该系统的不同浓度和组分的影响来优化这些剂量计的性能。 我们还表明，在辐照凝胶松弛发生通过磁化转移（MT）之间的自由水和不稳定的质子与半固体池中的聚合物接触。 我们将设计和验证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这种半固体质子池的大小随着剂量的增加而线性增加，并且我们将进行新的NMR和其他物理测量来验证该模型。 总的来说，我们的目标是生产出更好的凝胶用于实际应用，并更好地了解它们对辐射的反应。