Department of Radiation Oncology, New York University, Langone Medical Center & Laura and Issac Perlmutter Cancer Center, New York, NY, 10016, USA.
Standard Imaging Inc., Middleton, WI, 53562, USA.
Med Phys. 2019 May;46(5):2468-2476. doi: 10.1002/mp.13501. Epub 2019 Apr 8.
Small field dosimetry has been an active area of research for over a decade. It is now known that large dosimetric errors can be introduced if proper detectors or correction factors are not used. The International Atomic Energy Agency (IAEA) through the technical report series No. 483 provides guidelines for small field dosimetry procedures as well as correction factors for most detectors available in the market. The plastic scintillator detector (PSD) Exradin W1 has been found to have a correction factor close to unity; however, it is not designed for beam scanning. To overcome this limitation, the new PSD Exradin W2 has been developed to be used as a scanning as well as a relative dosimeter. Characterization of this detector in small field dosimetry is presented in this study.
A 6 MV beam from a Varian-Edge linac was used to collect data for the characterization of a W2 detector. Cerenkov light ratio (CLR) is corrected through a separate new electrometer system that comes with the W2 detector. The parameters investigated include the dose and dose rate linearity, beam profiles, percent depth dose (PDD), field output factors, and temperature response. The results were compared with Gafchromic film (EBT-3 film) for beam profiles. The field output factor and temperature response were compared to the Exradin W1 detector.
The dose linearity measured with 600 MU/min dose rate showed minimal variations (<0.5%) even for small MU, and similar results were seen for dose rate linearity. The comparison of field output factors between the W2 and W1 showed small differences for various depth and field sizes. The temperature response showed small variation when the temperature was varied from to . The slope was and for the W2 and the W1 detector, respectively. The differences in profiles are 0.5% in umbra and penumbra region for field size when compared to the EBT-3 film profile.
The W2 scintillator detector showed similar dosimetric and temperature properties to the W1 scintillator detector. The main advantage of the W2 detector among other plastic scintillators is the beam scanning capabilities that, combined with its correction factor of 1.0, make it an ideal detector for commissioning of SRS and SBRT techniques.
小野剂量学已经成为一个活跃的研究领域超过十年。现在已经知道，如果不使用适当的探测器或修正因子，会引入较大的剂量学误差。国际原子能机构（IAEA）通过技术报告系列 No.483 为小野剂量学程序以及市场上大多数可用探测器的修正因子提供了指导方针。塑料闪烁体探测器（PSD）Exradin W1 已被发现具有接近 1.0 的修正因子；然而，它不是为束扫描设计的。为了克服这个限制，新的 PSD Exradin W2 已被开发出来，可用于扫描和相对剂量计。本研究介绍了该探测器在小野剂量学中的特性。
使用瓦里安边缘直线加速器的 6MV 束收集 W2 探测器特性的数据。Cerenkov 光比（CLR）通过与 W2 探测器配套的单独的新静电计系统进行修正。研究的参数包括剂量和剂量率线性、束流剖面、百分深度剂量（PDD）、射野输出因子和温度响应。结果与束流剖面的 Gafchromic 胶片（EBT-3 胶片）进行了比较。与 Exradin W1 探测器相比，对射野输出因子和温度响应进行了比较。
以 600MU/min 剂量率测量的剂量线性度即使在小 MU 时也表现出最小的变化（<0.5%），并且剂量率线性度也有类似的结果。W2 和 W1 之间的射野输出因子比较显示，在各种深度和射野尺寸下，差异较小。当温度在 至 之间变化时，温度响应显示出较小的变化。斜率分别为 W2 和 W1 探测器的 和 。与 EBT-3 胶片的轮廓相比，当比较 射野尺寸时，轮廓的差异为 0.5%，在阴影和半影区域。
W2 闪烁体探测器的剂量学和温度特性与 W1 闪烁体探测器相似。W2 探测器相对于其他塑料闪烁体的主要优势是其束扫描能力，结合其 1.0 的修正因子，使其成为 SRS 和 SBRT 技术调试的理想探测器。
