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首页> 外文期刊>Medical Physics >Heterogeneity phantoms for visualization of 3D dose distributions by MRI-based polymer gel dosimetry.
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Heterogeneity phantoms for visualization of 3D dose distributions by MRI-based polymer gel dosimetry.

机译：通过基于MRI的聚合物凝胶剂量测定法可视化3D剂量分布的异质模型。

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摘要

Heterogeneity corrections in dose calculations are necessary for radiation therapy treatment plans. Dosimetric measurements of the heterogeneity effects are hampered if the detectors are large and their radiological characteristics are not equivalent to water. Gel dosimetry can solve these problems. Furthermore, it provides three-dimensional (3D) dose distributions. We used a cylindrical phantom filled with BANG-3 polymer gel to measure 3D dose distributions in heterogeneous media. The phantom has a cavity, in which water-equivalent or bone-like solid blocks can be inserted. The irradiated phantom was scanned with an magnetic resonance imaging (MRI) scanner. Dose distributions were obtained by calibrating the polymer gel for a relationship between the absorbed dose and the spin-spin relaxation rate of the magnetic resistance (MR) signal. To study dose distributions we had to analyze MR imaging artifacts. This was done in three ways: comparison of a measured dose distribution in a simulated homogeneous phantom with a reference dose distribution, comparison of a sagittally scanned image with a sagittal image reconstructed from axially scanned data, and coregistration of MR and computed-tomography images. We found that the MRI artifacts cause a geometrical distortion of less than 2 mm and less than 10% change in the dose around solid inserts. With these limitations in mind we could make some qualitative measurements. Particularly we observed clear differences between the measured dose distributions around an air-gap and around bone-like material for a 6 MV photon beam. In conclusion, the gel dosimetry has the potential to qualitatively characterize the dose distributions near heterogeneities in 3D.
机译：剂量计算中的异质性校正对于放射疗法治疗计划是必要的。如果检测器很大并且其放射学特征不等同于水，则异质性效应的剂量学测量会受到阻碍。凝胶剂量测定法可以解决这些问题。此外，它提供了三维（3D）剂量分布。我们使用填充了BANG-3聚合物凝胶的圆柱体模来测量异质介质中的3D剂量分布。体模具有空腔，可以在其中插入与水相当的或类似骨头的固体块。用磁共振成像（MRI）扫描仪扫描照射的体模。通过校准聚合物凝胶的吸收剂量与磁阻（MR）信号的自旋自旋弛豫率之间的关系来获得剂量分布。为了研究剂量分布，我们必须分析MR成像伪影。这是通过三种方式完成的：将模拟的均质体模中的测得剂量分布与参考剂量分布进行比较，将矢状扫描图像与从轴向扫描数据重建的矢状图像进行比较，以及MR和计算机断层扫描图像的配准。我们发现，MRI伪影会导致小于2 mm的几何变形，并且固体插入物周围的剂量变化小于10％。考虑到这些限制，我们可以进行一些定性的测量。特别是对于6 MV光子束，我们观察到气隙周围和骨状材料周围的剂量分布之间存在明显差异。总之，凝胶剂量学具有定性表征3D异质性附近剂量分布的潜力。

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