Optimizing shielding protocols in tube current modulation chest computed tomography: a phantom study

Growing public radiation protection awareness has heightened clinical focus on shielding. This study examines the relationship between shielding material placement, the overranging (OR), and scout image visibility in chest tube current modulation (TCM) computed tomography (CT). It analyzes changes in overall radiation dose within the patient imaging area and image quality of tissues at the scanning boundary near the shield to provide evidence for selecting optimal clinical shielding protocols.

This study utilized an anthropomorphic phantom to perform chest CT scans under TCM on a GE Revolution CT scanner. Lead shielding was placed intra- and extra-OR, categorized as scout-visible or invisible, to assess its impact on imaging area dose and changes in boundary organ image quality versus an unshielded control.

Intra-OR shields increased the radiation dose in the imaging area, with volume CT dose index (CTDI_vol) rising by up to 22.9% (range: 0.43%-22.9%) depending on the collimation-pitch combination, and caused degradation of image quality at the scan boundary (SNR and CNR reductions approximately twice those of the extra-OR shields group, with 50% of image scores ≤ 2, indicating limited diagnostic value). In contrast, extra-OR shields produced minimal changes: CTDI_vol increased by less than 3% in all cases, SNR/CNR reductions were below 10%, and all images scored ≥ 3 (meeting diagnostic requirements). Furthermore, scout-visible lead shielding was associated with increased radiation dose and reduced image quality. Conversely, scout-invisible lead shielding had a negligible effect on radiation dose but led to a more substantial degradation in image quality relative to the visible configuration.

Based on this phantom study, to optimize radiation protection and image quality in clinical chest TCM CT examinations, it is suggested that the shielding device be placed in the extra-OR region. However, as these findings derive from phantom experiments, further validation in clinical settings is warranted before routine application.