The paper describes instrumentation used at Czech Metrology Institute for measurement of photon fluence spectra directly in X-ray beams. Detector with a cadmium telluride (CdTe) sensor was characterized by means of energy resolution and precise energy calibration. The hole trapping effect in CdTe causing full-energy peak deformations in measured spectra was adopted consisting of analytical models of incomplete charge collection and carrier trapping based on Hecht equation. The detector collimator provided by the manufacturer was modified with additional tungsten shielding that effectively absorbs the majority of photons scattered in the collimator body resulting in significant improvement of the consistency of measured and Monte Carlo simulated detector response. The purpose-made alignment platform increased the accuracy of orientation of the collimator axis improving the measurement in high photon fluence rate beams using collimation disks with very small apertures (down to 100 μm in diameter). The adopted instrumentation and methods for X-ray beam spectrometry enabled to fulfil the requirements of the new ISO 4037:2019-ed.2.0 standard for reference metrology laboratories. Software-focused part dealing with Monte Carlo simulations and procedures for photon fluence spectra unfolding is summarized in [1].

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Two radiochromic gel dosimeters, Fricke-xylenol orange (FXO) gel and Turnbull Blue (TB) gel, were studied in the scope of the iMERA+ project ‘Increasing cancer treatment efficacy using 3D brachytherapy’ for their feasibility for the determination of relative 3D dose distribution of brachytherapy (BT) sources. Initially, the dose, dose rate and energy dependence of the gels were investigated. Subsequently, the gels were irradiated by a point low-dose-rate source IsoSeed I25.S16 (125I) and a high-dose-rate source GammaMed+ (192Ir) and scanned using optical computed tomography. Optical transmission images of irradiated gels were processed to obtain detailed 3D optical density maps inside the gels with voxel dimensions of 0.25 × 0.25 × 0.25 mm3. The radial dose function between 1.5 mm and 35 mm from the source and the anisotropy function at 10 mm radius were determined and compared with Monte Carlo calculations and TG-43 data, showing agreement mostly within the measurement uncertainty. Results revealed that the TB gel is feasible for measurements of the relative 3D dose distributions very close to the point BT source because it conserves sharp dose gradients as this gel does not suffer diffusion of dye created upon irradiation. On the other hand, FXO gel underestimates doses closer than 5 mm from the source due to diffusion effects, but it has a significantly higher sensitivity which enables convenient measurement of relative doses up to 35 mm from the source. Further development, especially on gel composition and corrections to optical CT images, is desirable.