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Identification and characterization of an optimal three-dimensional dosimetry system for remote auditing by the RPC.

机译：RPC远程审核的最佳三维剂量系统的识别和表征。

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摘要

Advanced treatment techniques currently used in radiation treatment require the use of a dosimeter capable of performing measurements with high spatial resolution in three-dimensions. The Radiological Physics Center (RPC) evaluates an institution's ability to deliver advance treatments through the use of anthropomorphic phantoms. The phantoms currently use film dosimetry to provide two-dimensional measurements in selected planes. Therefore, the RPC has a need for a three-dimensional dosimeter. The purpose of this project was to characterize several three-dimensional dosimeters and identify a formulation best suited for use by the RPC in an anthropomorphic phantom. Two polymer gel formulations, PAGAT and BANGRTMkit, and a radiochromic dosimeter, PRESAGE(TM), were investigated in this project.;An MR imaging protocol to perform spin-spin relaxation time (T2) measurements of the polymer gels was developed. Results showed that a multi-spin echo pulse sequence with at least 32 echoes and an echo time of 9 ms should be used to minimize the dose resolution of both gel formulations. A 64-echo multi-spin echo pulse sequence with a 9 ms echo time was used to perform T2 measurements of polymer gels in this project. Temperature measurements were made in a polymer gel during imaging to ensure the gel was not being heated thereby affecting the accuracy of the T2 measurements. A maximum temperature increase of 1.2 °C was measured and found to have no effect on the T2 measurements.;Each dosimetry formulation was characterized to determine the dose response, linearity, reproducibility, spatial stability, and dose resolution. PRESAGE dosimeters were imaged with optical computed tomography (OCT) after irradiation. Both MRI and OCT were used to identify the best-suited imaging modality for each polymer gel formulation. Established criteria for each parameter were used to evaluate each dosimeter's characteristics and to identify the dosimeter best-suited for use by the RPC. PAGAT gel imaged with OCT was identified as the dosimetry system to be used in an anthropomorphic phantom.;A conventional and IMRT treatment plan were developed for the RPC's head and neck phantom. An insert was manufactured to accommodate a polymer gel dosimeter. PAGAT polymer gel was used to measure both treatment plans. Film measurements were also made of both treatment plans. Film was able to achieve a pass rate of at least 93% for both the conventional and IMRT treatments. Pass rates no larger than 88% were achieved with gel. The gel irradiated with the IMRT treatment measured 35% more dose than calculated by the treatment plan. The gel irradiated with the conventional treatment also over-responded in certain regions.;The three-dimensional dosimeter is capable of providing measurements of the entire dose distribution from a single irradiation. Any plane within the distribution could be extracted from the gel measurements and compared to the treatment plan. However, PAGAT gel imaged with OCT was unable to provide comparisons with the treatment plan that are equivalent or better than those performed with film.
机译：当前在放射治疗中使用的高级治疗技术需要使用能够以高空间分辨率进行三维测量的剂量计。放射物理中心（RPC）评估机构通过使用拟人化体模提供先进治疗的能力。幻影当前使用胶片剂量法在选定平面中提供二维测量。因此，RPC需要三维剂量计。该项目的目的是表征几个三维剂量计，并确定最适合RPC在拟人模型中使用的配方。在此项目中，研究了两种聚合物凝胶配方PAGAT和BANGRTMkit，以及放射致变剂量计PRESAGETM。开发了一种MR成像协议，用于执行聚合物凝胶的自旋-旋弛豫时间（T2）测量。结果表明，应使用具有至少32个回波和9毫秒回波时间的多旋回波脉冲序列，以最小化两种凝胶制剂的剂量分辨率。在此项目中，使用具有9 ms回波时间的64回波多旋回波脉冲序列来执行T2测量。在成像过程中在聚合物凝胶中进行温度测量，以确保凝胶不被加热，从而影响T2测量的准确性。测量最大温度升高1.2°C，发现对T2测量没有影响。;每种剂量学配方的特征均在于确定剂量响应，线性，重现性，空间稳定性和剂量分辨率。照射后用光学计算机断层扫描（OCT）对PRESAGE剂量计进行成像。 MRI和OCT均用于确定每种聚合物凝胶配方的最适合的成像方式。为每个参数建立的标准用于评估每个剂量计的特性，并确定最适合RPC使用的剂量计。使用OCT成像的PAGAT凝胶被确定为拟人化体模中使用的剂量测定系统。;为RPC的头颈部体模制定了常规和IMRT治疗计划。制造插入件以容纳聚合物凝胶剂量计。 PAGAT聚合物凝胶用于测量两种治疗方案。还对两个治疗计划进行了胶片测量。对于常规处理和IMRT处理，胶片都能达到至少93％的通过率。用凝胶达到不超过88％的通过率。经IMRT处理的凝胶的剂量比治疗计划计算的剂量高35％。用常规处理方法辐照的凝胶在某些区域也反应过度。三维剂量计能够提供单次辐照的整个剂量分布的测量结果。分布范围内的任何平面都可以从凝胶测量值中提取出来，并与治疗计划进行比较。但是，用OCT成像的PAGAT凝胶无法与治疗方案进行比较，该方案与用胶片进行的等效或更好。

著录项

  • 作者

    Heard, Malcolm P.;

  • 作者单位

    The University of Texas Graduate School of Biomedical Sciences at Houston.;

  • 授予单位 The University of Texas Graduate School of Biomedical Sciences at Houston.;
  • 学科 Engineering Biomedical.;Biophysics Medical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 147 p.
  • 总页数 147
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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