Methodology for simulating x-ray sources of computed tomography systems using GATE 10 without manufacturer data

Objective.This study aims to implement and evaluate a source modeling method for Monte Carlo (MC) simulation of computed tomography (CT) systems in the absence of manufacturer data. This work enables simulation of realistic CT x-ray sources by integrating experimental measurements, particularly x-ray spectrometry, and to assess its applicability to single-energy CT scanners.Approach.An experimental method was implemented combining x-ray spectra using a CdTe spectrometer and a bowtie filter attenuation profile measured with an ionization chamber, and compared to manufacturer data. Two source models with different levels of complexity were created for GATE 10 simulations. First, a basic model single-spectrum (SS) using one energy spectrum measured on the beam axis combined with the attenuation profile was considered. Multi-spectra (MS) model incorporated additional spectra off-axis. For comparison, the SS model was used with manufacturer's data. These source models were evaluated by comparing simulations and measurements of half-value layers (HVLs) of aluminum at three voltages (80 kV, 120 kV and 140 kV), as well as CT dose index (CTDI) values measured on both head and body phantoms.Main results.HVL of SS and MS models showed a better agreement with measurements, yielding a mean difference of 4%. CTDI values derived from simulations based on MS source outperformed the other sources, with differences inferior to 7% with measurements. SS results had good agreement with measurements (<10%), but underestimated dose evaluation in some cases by up to 16%. The Manufacturer source showed the largest discrepancies, especially at 140 kV.Significance.This work highlighted that modeling spectral variations across the x-ray beam significantly improves CT source model. The proposed framework offers a replacement for manufacturer data when not available and participates in the foundation for using MC methods to support the integration of new CT systems.