Session Item

To characterize the response of small active detectors - suitable for measurements in a water phantom - in terms of energy and angular dependence at low energy X-ray beams and give recommendations for their use in electronic BrachyTherapy (eBT) dosimetry.

Three active small detectors, Exradin A26 chamber, IBA RAZOR Nano chamber, and PTW 60019 microDiamond were calibrated in terms of air kerma using the N (ISO 4037-1) and TW (DIN 6809-4) X-ray calibration series from 7.5 kV to 100 kV. The responses to mono-energetic photons and their uncertainties were determined using Bayesian parameter estimation, assuming a thin plate spline parametrized model. The angular dependence of the three detectors was also measured in air in a 180° range using the Zeiss INTRABEAM system (50 kV). For both, energy and angular response, the detectors were in parallel orientation.

The air kerma response functions for the three detectors are shown in Figure 1. The approach followed improves on the traditional procedure of associating the response to the mean energy of the corresponding spectra since it is consistent with 18 calibration qualities simultaneously. The in-air measured angular response of the detectors is shown in Figure 2, note that charge readings were normalized to the parallel incidence (0°).

The Exradin A26 chamber, IBA RAZOR Nano chamber and PTW microDiamond detector have been characterized in terms of their energy (6 keV to 70 keV) response to X-ray beams in air at both “N” and “TW” PTB series (18 qualities in total). The angular dependence of these detectors was also measured at intervals of 10° in a 180° range with the INTRABEAM at 50 kV and reported relative to the aligned incidence.

The procedure to determine the energy response can be expanded to other energy ranges and to other detectors and may lead to the creation of a detector-wise library avoiding the need of the user to re-calibrate the instrument for every new application and energy range.

The three detectors are promising candidates for 3D dose measurements of eBT sources in water. In particular, the A26 chamber exhibits an excellent angular response and a more flatter energy response to X-ray beams from above 20 keV compared to the other two detectors.

For the conversion of the detector’s response in terms of absorbed dose to water, MC simulations are currently been done by other partners of 18NRM02 PRISM-eBT project (see below).

Even when the response is far from flat, the knowledge of a reliable energy dependence curve allows the use of these detectors in the dosimetry of low photon energies, in eBT or in other applications of low energy X-ray conventional beam (as cell culture or small animal irradiators).

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.