Precision Kilovoltage x-Ray Spectra for Improved Benchmarking of Radiation Transport Simulations
Abstract
Purpose
In kV x-ray dosimetry, experimental spectral data can be used to benchmark Monte Carlo simulations and, if the experimental is suitably constrained, test the underlying interaction cross-section models used. This project aims to acquire accurate kV x-ray spectra, for well-established beam geometries and with known uncertainties, to add to the international catalogue of published spectra and thus provide a robust basis for model evaluation.
Methods
A HPGe detector was chosen as the spectrometer and collimation was carefully chosen to minimize scatter contributions, confirmed through sensitivity tests. Calibration of the spectrometer energy scale was carried out using Eu-152 and Am-241 gamma sources. Investigations included pulse pile-up (deadtime), positional sensitivity, and x-ray beam stability studies over days and weeks. Spectra were acquired for a range of kV and filtration settings, covering the energy range 50 kVp to 150 kVp. The focus was on acquiring different spectra to provide a comprehensive set of data for validating future Monte Carlo simulations.
Results
Beam current was optimized to minimize spectral artifacts caused by pulse pile-up while achieving a suitable SNR better than 1% across the full bremsstrahlung spectrum, for a bin-width of 20 eV. No systematic effects were seen across the range of energies measured, and consistent features (e.g., tungsten K-shell and L-shell lines) showed no significant drift over time. Testing indicated that ultra-long exposure times (several hours) were feasible to further refine spectral features.
Conclusion
The project has already yielded accurate data that can be used for testing of Monte Carlo simulations in the kilovoltage energy range. Measurements are ongoing to increase the number of different spectra acquired, with the intention of making the complete catalogue available to users of various radiation transport codes.