Abstract When dose measurement is carried out using an optically stimulated luminescence (OSL) dosimeter which uses a disk-shaped dosimeter in the diagnostic X-ray examination, angular dependence of the dosimeter should be taken into consideration. Angular dependence is the characteristic in which the detector response varies depending on incident angle of X-ray to the dosimeter and this becomes one of the causes of systematic uncertainty. In order to measure exposure dose accurately, it is important to reduce the systematic uncertainty caused by angular dependence. In this study, we propose two types of novel disk-shaped dosimeters for trials to reduce angular dependence: one is annular disk-shaped dosimeter, and the other is a composite-disk-shaped dosimeter. The commercially available dosimeter has a ϕ5 mm disk-shaped detection region which is composed of Al2O3;C. The annular disk-shaped dosimeter, which is proposed in this study, is a ϕ5 mm disk having a ϕ3 mm hole in it. Moreover, we propose a novel composite-disk-shaped dosimeter, which has two sensitive regions; a ϕ3 mm disk detection region is additionally inserted into the annular disk-shaped dosimeter. We performed Monte-Carlo simulation and experimentation using 40–140 kV X-rays to evaluate angular dependences and detection efficiencies of these dosimeters. In the simulation, incident angles of X-rays to the dosimeter varied every 15°. Experiments were performed under the same conditions. We also focused on the difference of angular dependence between 0° and 90°, and the ratio of responses at 90° divided by 0° was evaluated for analyzing the reduction rate of angular dependence. The results of ratios of the disk-shaped dosimeter, annular disk-shaped dosimeter and composite disk-shaped dosimeter were 82%, 89% and 88%, respectively. These results mean that the novel shaped dosimeters have better angular dependence compared with that of the original disk-shaped dosimeter. However, the detection efficiencies for disk-shaped dosimeter, annular disk-shaped dosimeter and composite disk-shaped dosimeter were 100%, 64% and 100%, respectively. From these facts, we concluded that the composite disk-shaped dosimeter can accomplish better angular dependence without loss of sensitivity. We verified that the characteristics of the conventionally-used disk-shaped dosimeter can be improved by adding some effort.

中文翻译：

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一种减少具有圆盘形检测区域的剂量计的角度依赖性的想法

摘要 当使用光学受激发光 (OSL) 剂量计进行剂量测量时，该剂量计在诊断 X 射线检查中使用盘形剂量计，应考虑剂量计的角度依赖性。角度相关性是探测器响应随 X 射线入射到剂量计的角度而变化的特性，这成为系统不确定性的原因之一。为了准确测量暴露剂量，减少由角度依赖性引起的系统不确定性很重要。在这项研究中，我们提出了两种新型盘形剂量计用于试验以减少角度依赖性：一种是环形盘形剂量计，另一种是复合盘形剂量计。市售的剂量计有一个由 Al2O3;C 组成的 φ5 mm 圆盘形检测区域。本研究中提出的环形盘形剂量计是一个φ5 mm 的圆盘，上面有一个φ3 mm 的孔。此外，我们提出了一种新型复合盘形剂量计，它具有两个敏感区域；一个 φ3 mm 的圆盘检测区域被额外插入到环形圆盘形剂量计中。我们使用 40-140 kV X 射线进行了蒙特卡罗模拟和实验，以评估这些剂量计的角度依赖性和检测效率。在模拟中，X 射线到剂量计的入射角每 15° 变化一次。实验在相同条件下进行。我们还关注了 0° 和 90° 之间角度依赖性的差异，并且评估90°处的响应除以0°的比率以分析角度依赖性的降低率。盘形剂量计、环形盘形剂量计和复合盘形剂量计的比值结果分别为82%、89%和88%。这些结果意味着与原始盘形剂量计相比，新型形状的剂量计具有更好的角度依赖性。而盘形剂量计、环形盘形剂量计和复合盘形剂量计的检测效率分别为100%、64%和100%。根据这些事实，我们得出结论，复合盘形剂量计可以在不损失灵敏度的情况下实现更好的角度依赖性。我们验证了可以通过增加一些努力来改善传统使用的盘形剂量计的特性。