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Characterization of small active detectors for electronic brachytherapy (eBT) dosimetry performed


Figure: Photographs and radiographs of the 3 detectors. From left to right: Exradin A26 ionization chamber, IBA RAZOR Nano ionization chamber and PTW 60019 microDiamond.

Three active detectors, Exradin A26 ionization chamber, IBA RAZOR Nano ionization chamber, and PTW 60019 microDiamond, see figure, were characterized for their use in electronic BrachyTherapy (eBT) dosimetry. The detectors were calibrated in terms of air kerma at the PTB using the ISO “N” (narrow) and “TW” (therapy) X‑rays series from 7.5 kV to 100 kV. The responses to mono‑energetic photons and their uncertainties were determined with Bayesian parameter estimation, assuming a model that incorporated smoothness via a spline function. The response functions obtained this way are consistent with 18 calibration qualities simultaneously. This approach improves on the traditional procedure of associating the response to the mean energy of the corresponding spectra. The energy responses (with uncertainties) were obtained in 0.25 keV energy steps from 6 keV to 70 keV. While there were differences in magnitude due to their sizes and the nature of their active volumes, the energy responses of the 3 detectors follow a similar relative behavior. Even when the response is far from flat at low energies, i.e., below about 20 keV, the determination of reliable energy dependence curves enables the use of these detectors for dosimetry in the near‑field of eBT units. The angular dependence of the three detectors with respect to beam incidence was also measured in air in a 180° range in steps of 10° using the Zeiss INTRABEAM system (50 kV). For both, energy and angular response characterization, the detectors were aligned in parallel with the beam axis, since this is the expected orientation in further measurements of absorbed dose distribution in water around eBT sources at PTB. This work serves for providing traceability for detectors and measurement procedures for the determination of 3D dose distributions as part of the ongoing European EMPIR project “Primary standards and traceable measurement methods for X‑ray emitting electronic brachytherapy devices” (PRISM‑eBT)”.

The results of this investigation will be submitted to a peer‑reviewed journal.


This research was accomplished within the framework of project 18NRM02 PRISM‑eBT that has received funding from the EMPIR programme co‑financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.


Fernando Garcia Yip, Department 6.3, Working group 6.34

Thorsten Schneider, Department 6.3, Working group 6.34

Rolf Behrens, Department 6.3, Working group 6.34