Measurement of the half-value layer for CT systems in a single-rotation technique: Reduction of stray radiation with lead apertures

[Display omitted] •A new technique was introduced to measure the HVL during a single gantry rotation.•Five K̇air peaks/K̇air declines were used for the calculation of HVL.•The accuracy of the new technique was comparable to that of a conventional method.•The lead apertures were useful to increase the accuracy of the HVL measurements.•There is no need for X-ray tubes to be fixed in the service mode. This study aimed to compare two methods of assessing the half-value layer (HVL) for computed tomography scanners in a single-rotation technique with and without lead apertures (SRTLA / SRT). A 0.6 cc real-time ionization chamber was suspended freely in the air at the isocenter, and six sheets of lead (130 × 170 × 2 mm) were placed at the bottom of the gantry cover, forming five apertures each having a width of 16 mm (SRTLA geometry). Four aluminum plates (100 × 100 mm2; 2.0, 4.0, 6.0, and 8.0 mm thick) were placed on these apertures. Air-kerma rate profiles (K̇air) in the spiral mode were measured at tube potentials of 80, 100, 120, and 135 kVp, a tube current of 100 mA, a nominal beam width of 32.0 mm, and a rotation time of 1.5 s. Thereafter, all lead sheets were removed, and these same measurements were taken to investigate the errors of the HVLs (SRT geometry). HVLs using the SRTLA and SRT were compared with those obtained through a conventional localization technique. The HVLs measured in the SRTLA/SRT at 80, 100, 120, and 135 kVp were 3.37/3.50, 4.24/4.47, 5.22/5.44, and 5.90/6.17 mm, respectively. The differences between these values and those obtained through the conventional technique were 0.09/0.22, 0.02/0.25, 0.05/0.27, and −0.01/0.26 mm, respectively. The accuracies of the HVLs of the SRTLA were similar to those of the conventional technique. The lead apertures under the aluminum plates would help reduce the number of inaccurate HVL measurements.