Experimental Comparison of Half-Value Layer Measurements Using a Solid-State X-ray Meter and an Ionization Chamber in General Radiography

Background: Half-value layer (HVL) is a fundamental descriptor of diagnostic X-ray beam quality.This study compared HVL measurements obtained with a solid-state X-ray meter (Cobia SMART, RTI Group, Mölndal, SWE) and an ionization-chamber dosimetry system across multiple tube-voltage and measurement-distance conditions.Methods: Measurements were performed at 60, 80, 100, and 120 kV and source-to-detector distances (SDDs) of 100, 150, and 200 cm.The corresponding exposure settings were 50, 110, and 200 mAs, respectively.Three independent ionization-chamber HVL determinations and three Cobia readings were obtained for each condition.Agreement was evaluated using absolute and percentage differences and descriptive Bland-Altman analysis.A partial uncertainty assessment incorporated repeatability-based type A uncertainty and the 0.1 mm Al recording resolution of the Cobia data.Results: The ionization-chamber coefficient of variation ranged from 0.09% to 2.38%, with a mean of 1.16%.Cobia showed identical recorded triplicate values at each tube voltage, with HVLs of 2.1, 2.9, 3.7, and 4.6 mm Al at 60, 80, 100, and 120 kV, respectively.Eleven of the 12 paired conditions differed by no more than 0.20 mm Al.The largest discrepancy occurred at 120 kV and 150 cm, where the difference was +0.466 mm Al (+11.27%).Bland-Altman analysis yielded a mean bias of +0.057 mm Al, with descriptive 95% limits of agreement from -0.240 to +0.353 mm Al.Conclusions: Cobia SMART demonstrated stable recorded HVL values and generally close agreement with the ionization-chamber method across most tested conditions.However, a notable discrepancy was observed at 120 kV and 150 cm, indicating that agreement under one exposure condition should not be generalized across the entire diagnostic range.Cobia SMART may be a practical tool for rapid routine HVL quality-control measurements, with periodic comparison against a calibrated reference dosimetry system advisable after changes in measurement geometry or when unexpected HVL values are obtained.