GEL FOR 3D DOSIMETRY BY OPTICAL TOMOGRAPHIC DENSITOMETRY

本项目旨在开发一种新型的组织等效凝胶电离辐射剂量计，该剂量计能够使用光学层析密度测定法产生高分辨率和精确的三维剂量分布数据。剂量-响应机制依赖于辐射吸收部位凝胶中瑞利散射微粒的产生，在那里分散在凝胶中的丙烯酸单体被聚合。准直光通过光混浊介质时的吸收和散射会产生光强的净衰减，这种光强可以测量，并且与剂量直接相关。测量光密度在不同方向上的投影可以用来重建凝胶内辐射剂量的分布。10gy量级的剂量可以在<1mm的空间分辨率下测量。在以前的工作中，已经研究了凝胶的MRI特性，并非常成功地用于创建3D剂量图，但是使用更简单的光学方法读取凝胶存储的剂量分布具有显着的优势。该凝胶将广泛应用于放射治疗实践，均匀和拟人化幻影的三维测量，计算机治疗计划的确认以及质量保证程序。第一阶段的目标是设计和评估一种方便和廉价的制备用于光密度测定的原型聚合物凝胶剂量计的方案，证明其稳定性和可重复性以及剂量响应的空间均匀性，并评估构建用于重建3D剂量分布的低成本台式光学扫描仪的可行性。这些研究将为第二阶段开发更高效的聚合物凝胶和光学读取器奠定基础。

This project aims to develop a novel, tissue-equivalent gel-dosimeter of ionizing radiation, which is capable of producing highly-resolved and accurate data on three dimensional dose distributions using optical tomographic densitometry. The dose-response mechanism relies on the production of Rayleigh scattering micro-particles in the gel at the site of radiation absorption, where acrylic comonomers dispersed in the gel are polymerized. Absorption and scattering of collimated light passing through the optically turbid medium produces a net attenuation of light intensity that can be measured and is directly related to the dose. Measurements of the projections of the optical density into different directions can be used to reconstruct the distribution of radiation doses within the gel. Doses of the order of 10 Gy can be measured with a spatial resolution <1mm. In previous work, the MRI properties of the gel have been investigated and used very successfully to create 3D dose maps, but there are significant advantages to the use of a simpler optical method of reading the dose distribution stored by the gel. The gel will find widespread use in radiation therapy practice, for 3D measurements in homogeneous and anthropomorphic phantoms, confirmation of computerized treatment planning and in quality assurance procedures. The goals of Phase I are to devise and evaluate a protocol for convenient and inexpensive preparation of a prototype polymer-gel dosimeter optimized for optical densitometry, to demonstrated its stability and reproducibility as well as spatial uniformity of the dose-response, and to evaluate the feasibility of constructing a low-cost bench top optical scanner for the reconstruction of 3D dose distributions. These studies will prepare the ground for the development of more efficient polymer-gels and an optical reader in Phase II. PROPOSED COMMERCIAL APPLICATION: Estimated 5000 polymer-gels could be distributed annually. This estimate is based upon (a) 30 new accelerators per year, and 40 X-ray and electron beam field; (b) over 3000 existing treatment machines will use 10 gels per year for dosimetry; (c ) research centers might use 5 gels annually for non-routine dose distributions. The annual sales of the gels alone could produce $1,000,000 sales. In addition, if the optical device is available for a cost of $50,000, then 20 such devices per year could be sold, comparable to the number of "water-tank" systems that are in current use.