Purpose: This study evaluated various methods for determining the half-value layer (HVL) of kilovoltage (kV) beams produced by the Varian TrueBeam STx on-board imager. By comparing these methods with the standard ionization chamber approach, the study aimed to identify practical solutions for HVL determination and dosimetric characterization of kV beams, particularly in resource-limited settings.
Methods: HVLs for kV beams (40–140 kVp) were measured using an Exradin A12 ionization chamber and a Piranha MULTI meter. The ionization chamber measurements adhered to American Association of Physicists in Medicine Task Group 61 guidelines and served as the reference standard. Additionally, HVL values were calculated using two model-based approaches: SpekPy (a Python-based tool) and Monte Carlo (MC) simulations using Geant4 and GATE. The results from these methods were compared to assess consistency and reliability.
Results: Deviations across all methods were generally below 4%. At 40 kV, the most significant discrepancies were attributed to lower signal levels from the ionization chamber. The consistency between the model-based methods and experimental measurements demonstrates the reliability of these alternative approaches for HVL determination.
Conclusions: Although the ionization chamber remains the gold standard, the Piranha MULTI meter and model-based methods, i.e., SpekPy and MC simulations, have shown promise as viable alternatives, especially in resource-constrained settings. These in silico approaches also offer advantages in convenience and accuracy, supporting their potential for broader future applications.

KeywordsHalf-value-layer, Kilovoltage X-ray beam, Piranha, Monte Carlo simulation, SpekPy