Fakultät Physik, Technische Universität Dortmund, Otto-Hahn-Str. 4a, 44221, Dortmund, Germany.
Med Phys. 2017 Sep;44(9):4900-4909. doi: 10.1002/mp.12374. Epub 2017 Jul 18.
Plastic scintillation detectors are used for dosimetry in small radiation fields with high dose gradients, e.g., provided by β-emitting sources like Ru/ Rh eye plaques. A drawback is a background signal caused by Cerenkov radiation generated by electrons passing the optical fibers (light guides) of this dosimetry system. Common approaches to correct for the Cerenkov signal are influenced by uncertainties resulting from detector positioning and calibration procedures. A different approach to avoid any correction procedure is to suppress the Cerenkov signal by replacing the solid core optical fiber with an air core light guide, previously shown for external beam therapy. In this study, the air core concept is modified and applied to the requirements of dosimetry in brachytherapy, proving its usability for measuring water energy doses in small radiation fields.
Three air core detectors with different air core lengths are constructed and their performance in dosimetry for brachytherapy β-sources is compared with a standard two-fiber system, which uses a second fiber for Cerenkov correction. The detector systems are calibrated with a Sr/ Y secondary standard and tested for their angular dependence as well as their performance in depth dose measurements of Ru/ Rh sources.
The signal loss relative to the standard detector increases with increasing air core length to a maximum value of 58.3%. At the same time, however, the percentage amount of Cerenkov light in the total signal is reduced from at least 12.1% to a value below 1.1%. There is a linear correlation between induced dose and measured signal current. The air core detectors determine the dose rates for Ru/ Rh sources without any form of correction for the Cerenkov signal.
The air core detectors show advantages over the standard two-fiber system especially when measuring in radiation fields with high dose gradients. They can be used as simple one-fiber systems and allow for an almost Cerenkov-free scintillation dosimetry of brachytherapy β-sources.
塑料闪烁探测器用于测量具有高剂量梯度的小辐射场中的剂量，例如由β发射源（如 Ru/ Rh 眼贴）提供的剂量。缺点是由通过该剂量测量系统的光纤（光导）的电子产生的切伦科夫辐射引起的背景信号。校正切伦科夫信号的常用方法受到探测器定位和校准程序不确定度的影响。避免任何校正过程的另一种方法是通过用空气芯光导代替固体芯光纤来抑制切伦科夫信号，这在以前的外束治疗中已经证明。在这项研究中，对空气芯概念进行了修改，并应用于近距离治疗中的剂量测量要求，证明了其在小辐射场中测量水能量剂量的可用性。
构建了三个具有不同空气芯长度的空气芯探测器，并将其在近距离治疗β源剂量测量中的性能与使用第二根光纤进行切伦科夫校正的标准双光纤系统进行了比较。探测器系统使用 Sr/ Y 次级标准进行校准，并对其角度依赖性以及在 Ru/ Rh 源深度剂量测量中的性能进行了测试。
与标准探测器相比，信号损失随空气芯长度的增加而增加，最大可达 58.3%。然而，与此同时，总信号中的切伦科夫光的百分比从至少 12.1%降低到 1.1%以下。感应剂量与测量的信号电流之间存在线性相关性。空气芯探测器可以在不校正切伦科夫信号的情况下确定 Ru/ Rh 源的剂量率。
空气芯探测器与标准双光纤系统相比具有优势，特别是在测量具有高剂量梯度的辐射场时。它们可以用作简单的单光纤系统，并允许对近距离治疗β源进行几乎无切伦科夫的闪烁剂量测量。
