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: 6693762
• 负责人: JOHN C GORE
• 金额: $ 30.24万
• 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/6693762
• 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.

研究旨在开发改进的聚合物凝胶，该凝胶可用于精确测量三个维度的辐射剂量分布。 聚合物凝胶剂量计在我们的实验室首次开发用于与MRI一起使用，该剂量记录了由水凝胶中单体混合物照射产生的水质子的NMR松弛时间的变化。 这样的凝胶是组织等效的，并在三个维度具有高空间分辨率的三维中提供了独特而准确的测量。 但是，在实践中使用当前可用的聚合物凝胶的使用仍然存在重大问题，这些凝胶限制了其更广泛的使用。 其中包括制备和储存凝胶的困难，必须制作并保持低氧之前，直到使用并因此不能将其倒入塑料或任意容器中：它们的可变灵敏度，这在很大程度上源于痕量的氧气影响，从而抑制其反应：以及有限的剂量响应，基于衡量符合错误的T2值的变化。 提出的研究将导致明显改善的凝胶，这些凝胶更敏感，更稳定，并且可以在正常的气氛中和医院物理学家的任何容器中制成，而无需采用特殊程序。 在初步研究中，我们在房间空气中产生了比目前凝胶更敏感的凝胶。 这些使用基于铜离子和抗坏血酸的新型引发剂系统，该系统与分子氧结合并需要分子氧气在凝胶被照射时开始聚合。 我们将通过探索该系统的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，辐照凝胶中的松弛是通过与聚合物中半固体池接触的游离水和不稳定质子之间的磁化转移（MT）发生的。 我们将设计和验证MT敏感序列的性能，这些序列避免了T2测量的陷阱，以成像凝胶以提取准确的剂量信息。 我们还假设，聚合物凝胶的剂量反应只是反映了该半固体质子池的线性增加，并增加了剂量，我们将执行新颖的NMR和其他物理测量，以验证该模型。 总体而言，我们旨在为实用应用产生大量改进的凝胶，并对它们对辐射的反应更好，更定量的了解。