Using the radioluminescence light of solid state probes coupled to long and flexible fibers for dosimetry in radiotherapy offers many advantages in terms of probe size, robustness and cost efficiency. However, especially in hadron fields, radioluminophores exhibit quenching effects dependent on the linear energy transfer. This work describes the discovery of a spectral shift in the radioluminescence light of beryllium oxide in dependence on the residual range at therapeutic proton energies. A spectrally resolving measurement setup has been developed and tested in scanned proton fields. It is shown that such a system can not only quantitatively reconstruct the dose, but might also give information on the residual proton range at the point of measurement.

A detector system for the purpose of quality assurance in radiation therapy is being developed and measurements in proton fields are presented. It is based on a beryllium oxide probe coupled to an optical fiber. Radioluminescence in the material generates photons, whose number is proportional to the dose absorbed in the probe. The photons are detected by very sensitive time resolving single photon counting heads. Diameter and height of the beryllium oxide probe amount 1 mm each. The probe was exposed to proton fields at a research and clinical accelerator. With rising linear energy transfer, saturation effects in the light signal. In consequence, the measuring signal is not proportional to the reference dose and needs to be corrected especially in the last 10 mm of the proton range. For this purpose, spectral changes of the radioluminescence photons, which depend on the linear energy transfer of the protons, were used to set up a correction factor. Hereby, it was possible to achieve a deviation of 2.3 % compared to an ionization chamber. Furthermore, beam profiles and linear energy transfer across the profile were studied.

The use of an active measurement system to localize contamination in concrete structures of nuclear facilities offers advantages such as an easy on-site analysis within a short measurement time. A measuring system based on a scintillation crystal connected to a long optical fiber with a large diameter could satisfy the demands of a measuring system for gamma-ray spectroscopy in boreholes. This work describes the development of a gamma-ray spectroscopy system using a fiber optic radiation sensor. A prototype was built with a GAGG scintillation crystal, which could reach an energy resolution of 33% at the 662-keV gamma-ray emission energy of 137 Cs. A minimal time for the detection of a contamination of a 137 Cs source with an activity of 21 kBq and a layer of 6-cm concrete between sensor and radiation source was determined to be under 1 min with three different evaluation methods. They were based on the decision threshold and the Kolmogorov–Smirnov test corresponding to the energy distribution and the distribution of time differences between detector events. In addition, it was possible to estimate the distance of a point-like source from the sensor by establishing a further analysis parameter comparing different energy regions of a spectrum.

The present work displays the progress in dose and dose rate measurements in proton beams using the luminescence of beryllium oxide (BeO). Preceding experiments carried out in a 190 MeV scattered proton beam have shown that the responses of the optically stimulated luminescence (OSL) and radio-luminescence (RL) of BeO differ in their LET dependency. This can be exploited to perform accurate dose measurements as well as the determination of the LET value within the depth dose profile of a mono-energetic proton beam. In the current work a redesigned and optimized OSL-RL measurement setup is used to perform both OSL and RL readings sequentially with the very same BeO detector with a high optical stimulation and detection efficiency. The BeO detector (<; 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) is stimulated and read out remotely using a pure silica core optical light guide coupling which transmits the stimulation light of a blue high power LED as well as the luminescence light that is detected by a single photon sensor. Additional optical filtering and a beam splitter are applied to separate the high intensity stimulation from the luminescence light. The system was tested measuring depth dose profiles of a mono-energetic proton beam and in the mixed LET field of a spread out Bragg peak similar to clinical conditions in proton therapy. Further investigations with a monochromator setup show the LET dependency of the RL spectrum.

Single photon detection applied to optically stimulated luminescence (OSL) dosimetry is a promising approach due to the low level of luminescence light and the known statistical behavior of single photon events. Time resolved detection allows to apply a variety of different and independent data analysis methods. Furthermore, using amplitude modulated stimulation impresses time- and frequency information into the OSL light and therefore allows for additional means of analysis. Considering the impressed frequency information, data analysis by using Fourier transform algorithms or other digital filters can be used for separating the OSL signal from unwanted light or events generated by other phenomena. This potentially lowers the detection limits of low dose measurements and might improve the reproducibility and stability of obtained data. In this work, an OSL system based on a single photon detector, a fast and accurate stimulation unit and an FPGA is presented. Different analysis algorithms which are applied to the single photon data are discussed.

The present work investigates methods for dose and dose rate measurements in proton beams using the luminescence of beryllium oxide (BeO). Experiments are carried out to determine the response of the optically stimulated luminescence (OSL) of BeO as well as the radioluminescence (RL) of BeO within the depth dose profile of a 190 MeV scattered proton beam. The acquired data is compared to an ionization chamber reference and a Monte Carlo simulation. Both dose readings from the RL and OSL measurements show accurate values in the entrance path with an increasing underestimation in the high LET region of the Bragg peak. The amount of this quenching is different for RL and OSL so that the ratio of RL to OSL dose measurements opens venues to correct the measurements to the accurate dose.

This work presents a fiber optical dose rate measurement system based on the radioluminescence and optically stimulated luminescence of beryllium oxide. The system consists of a small, radiation sensitive probe which is coupled to a light detection unit with a long and flexible light guide. Exposing the beryllium oxide probe to ionizing radiation results in the emission of light with an intensity which is proportional to the dose rate. Additionally, optically stimulated luminescence can be used to obtain dose and dose rate information during irradiation or retrospectively. The system is capable of real time dose rate measurements in fields of high dose rates and dose rate gradients and in complex, narrow geometries. This enables the application for radiation protection measurements as well as for quality control in radiotherapy. One inherent drawback of fiber optical dosimetry systems is the generation of Cherenkov radiation and luminescence in the light guide itself when it is exposed to ionizing radiation. This so called “stem” effect leads to an additional signal which introduces a deviation in the dose rate measurement and reduces the spatial resolution of the system, hence it has to be removed. The current system uses temporal discrimination of the effect for radioluminescence measurements in pulsed radiation fields and modulated optically stimulated luminescence for continuous irradiation conditions. This work gives an overview of the major results and discusses new-found obstacles of the applied methods of stem discrimination.

In this work the stem-removal by gated detection of radioluminescence signals in pulsed radiation fields is applied to a BeO-based fiber optical dosimetry system for the first time. The short luminescence life time of BeO, which is around 27 mu s at room temperature, requires a fast detection system. Measurements with 10 ns temporal resolution have been carried out in different radiation fields of a medical linear accelerator within a mean dose rate range of 33-550 cGy/min and for field sizes of 10 x 10 and 34 x 34 cm(2). The influence of the dose rate and the length of irradiated light guide on the temporal signal shape of the luminescence have been investigated. Based on the information of the raw data, methods to remove the stem part of the signal in real time have been tested. (C) 2017 Elsevier Ltd. All rights reserved.