Abstract：
The polymer gel dosimeter has been proposed for use as a 3D dosimeter for complex dose distribution measurement of high dose-rate (HDR) brachytherapy. However, various shapes of catheter/applicator for sealed radioactive source transport used in clinical cases must be placed in the gel sample. The absorbed dose readout for the magnetic resonance (MR)-based polymer gel dosimeters requires calibration data for the dose-transverse relaxation rate (R2) response. In this study, we evaluated in detail the dose uncertainty and dose resolution of three calibration methods, the multi-sample and distance methods using the Ir-192 source and the linear accelerator (linac) method using 6MV X-rays. The use of Ir-192 sources increases dose uncertainty with steep dose gradients. We clarified that the uniformly irradiated gel sample improved the signal-to-noise ratio (SNR) due to the large slice thickness of MR images and could acquire an accurate calibration curve using the linac method. The curved tandem and ovoid applicator used for intracavitary irradiation of HDR brachytherapy for cervical cancer were reproduced with a glass tube to verify the dose distribution. The results of comparison with the treatment planning system (TPS) calculation by gamma analysis on the 3%/2 mm criterion were in good agreement with a gamma pass rate of 90%. In addition, the prescription dose could be evaluated accurately. We conclude that it is easy to place catheter/applicator in the polymer gel dosimeters, making them a useful tool for verifying the 3D dose distribution of HDR brachytherapy with accurate calibration methods.
摘要：
聚合物凝胶剂量计已被提议用作3D剂量计，用于高剂量率（HDR）近距离放射治疗的复杂剂量分布测量。然而,在临床病例中使用的用于密封放射源运输的各种形状的导管/涂药器必须放置在凝胶样品中。基于磁共振（MR）的聚合物凝胶剂量计的吸收剂量读数需要剂量-横向弛豫率（R2）响应的校准数据。在这项研究中,我们详细评估了三种校准方法的剂量不确定度和剂量分辨率，使用Ir-192源的多样本和距离方法以及使用6MVX射线的线性加速器（直线加速器）方法。Ir-192源的使用增加了具有陡峭剂量梯度的剂量不确定性。我们澄清说，均匀辐照的凝胶样品由于MR图像的大切片厚度而提高了信噪比（SNR），并且可以使用直线加速器方法获得准确的校准曲线。用玻璃管再现了用于HDR近距离放射治疗宫颈癌腔内照射的弯曲串联和卵形涂药器，以验证剂量分布。与通过3％/2mm准则进行伽马分析的治疗计划系统（TPS）计算的结果进行比较，伽马通过率为90％。此外,处方剂量可以准确评估。我们得出的结论是，将导管/涂药器放置在聚合物凝胶剂量计中很容易，使它们成为使用精确校准方法验证HDR近距离放射治疗的3D剂量分布的有用工具。
