Inaccurate table height setting affects the organ-specific radiation dose in computed tomography

Abstract

Purpose: We aimed to prove that the locally absorbed doses in tissues and organs are affected by inaccurate table height in computed tomography.

Materials and methods: We compared the volume CT dose index (CTDI_vol) and the absorbed doses using an anthropomorphic phantom combined with a breast phantom. The phantom was set at the gantry center, from which the table height was changed every 20 mm between-40 mm and 40 mm. Data acquisition was performed using auto table height correction (AHC) for each table height. The CTDI_vol was obtained from the CT console and the tube current value for each image slice (DICOM tag: 0018, 1151). The absorbed dose was measured by a glass dosimeter that was implanted at various positions in the phantom.

Results: The tube current values in the lung were lower at a table height of + 40 mm than those at other heights. The CTDI_vol was slightly lower at + 40 mm than at the center (12.78 mGy vs. 13.42 mGy, p < 0.05). The CTDI_vol values were almost the same at the other table heights (13.30-13.40 mGy). The absorbed doses at the lens and mammary gland were significantly different from those at the gantry center (-27.27%-17.77% and -24.31%-12.83%, respectively). Compared with the center, both the lens and mammary gland had higher absorbed doses at a table height of -40 mm.

Conclusion: The absorbed dose was affected by the table height, but the CTDI_vol was maintained by AHC. The operator should appropriately position patients even when using AHC.

Keywords: Absorbed dose; Auto couch height positioning compensation; CT imaging; Output dose; Positioning.