Dosimetric properties and radiation hardness of the storage phosphor europium doped potassium chloride for radiation therapy dosimetry

DissertationMultidimensional reusable dosimeters are extremely important for characterizing the complex dose distributions associated with modern radiation therapy techniques, such as intensity modulated radiation therapy (IMRT). In particular, reusability provides medical physicists a degree of confidence in dosimetric measurements through the acquisition of benchmarking datasets and through long-term, repeated use and performance monitoring. Yet a dosimeter that has all of the properties desired for radiation therapy use, such as reusability, high spatial resolution, and water-equivalence, is not currently available. The results of this dissertation demonstrate that the reusable storage phosphor europium doped potassium chloride, KCl:Eu2+, has the potential to significantly advance the state-of-the-art in radiation therapy dosimetry. Prototype chip and panel dosimeters were fabricated according to well-developed materials science processes. Dosimetric properties were studied by reading photostimulated luminescence (PSL) after irradiation with a laboratory optical system. Sensitivity was independent of dose rate and beam energy for commonly used therapy beams. Over-response to low-energy scattered photons was comparable to conventional radiographic film and reduced with lead foils. No significant changes in the PSL process were detected up to 5000 Gy dose history, indicating that the material could be reused up to 2500 times at 2 Gy per use, as in, for example, patient-specific IMRT quality assurance. Investigations of KCl:Eu2+ panel dosimeters show that sub-millimeter spatial resolution is achievable and that micron-scale dosimeters have a water-equivalent dose response with sufficient sensitivity over clinically relevant dose ranges. In conclusion, KCl:Eu2+ is demonstrated to have many desirable properties for radiation therapy dosimetry. This study provides a practical and theoretical knowledge base that advances and supports future KCl:Eu2+ dosimetry research

Two-dimensional high spatial-resolution dosimeter using europium doped potassium chloride: a feasibility study

Recent research has shown that KCl:Eu²⁺ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. This work reports the authors' attempts to fabricate 2D KCl:Eu²⁺ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. X-ray diffraction analysis showed that a 10 µm thick PVD sample was composed of highly crystalline KCl. No additional phases were observed, suggesting that the europium activator had been completely incorporated into the KCl matrix. Photostimulated luminescence and photoluminescence spectra suggested that F (Cl(-)) centers were the electron storage centers post x-ray irradiation and that Eu²⁺ cations acted as luminescence centers in the photostimulation process. The 150 µm thick casted KCl:Eu²⁺ SPF showed sub-millimeter spatial-resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu²⁺ and 80% low Z polymer binder exhibited almost no energy-dependence in a 6 MV beam. KCl:Eu²⁺ pellet samples showed a large dynamic range from 0.01 cGy to 60 Gy dose-to-water, and saturated at approximately 500 Gy as a result of KCl's intrinsic high radiation hardness. Taken together, this work provides strong evidence that KCl:Eu²⁺-based SPF with associated readout apparatus could result in a novel electronic film system that has all the desirable features associated with classic radiographic film and, importantly, water equivalence and the capability of permanent identification of each detector

Theoretical and empirical investigations of KCl:Eu2+ for nearly water-equivalent radiotherapy dosimetry

Purpose: The low effective atomic number, reusability, and other computed radiography-related advantages make europium doped potassium chloride (KCl:Eu2+) a promising dosimetry material. The purpose of this study is to model KCl:Eu2+ point dosimeters with a Monte Carlo (MC) method and, using this model, to investigate the dose responses of two-dimensional (2D) KCl:Eu2+ storage phosphor films (SPFs)