[Temporal Changes in Volume CT Dose Index in Radiation Dose Management for X-ray CT Scanners].

Purpose: The purpose of this study was to understand the temporal changes in the volume CT dose index (CTDI_vol) and Image noise.

Methods: The following 3 types of X-ray CT scanners were used: Aquilion PRIME Beyond Edition (CANON MEDICAL SYSTEMS, Tochigi, Japan; referred to as System A), Aquilion PRIME SP (CANON MEDICAL SYSTEMS; referred to as System B), and SOMATOM Definition Flash (Siemens Healthineers, Erlangen, Germany; referred to as System C). The CTDI_vol was measured by placing an ion chamber in an acrylic phantom. The image noise was calculated as the standard deviation (SD) measured at center locations on the reconstructed water phantom image. Temporal changes were evaluated using relative errors. Relative errors were calculated by dividing the difference between the measured value for each month and the reference value by the reference value. The reference value was defined as the displayed value for CTDI_vol evaluation and the first measured value for SD evaluation. The study period was from June 2023 to May 2024, with measurements taken once a month for a total of 12 times.

Results: The mean relative errors of CTDI_vol were -0.071±0.017 for System A, 0.029±0.014 for System B, and -0.090±0.008 for System C. The mean relative errors of SD were 0.007±0.004 for System A, 0.002±0.004 for System B, and 0.023±0.013 for System C.

Conclusion: The mean relative error of CTDI_vol was less than 10% and that of SD was less than 3%. The results of this study suggest the need for radiation dose management by monitoring the temporal changes in CTDI_vol.