Breast bismuth shielding in coronary CT angiography: To shield or not to shield?

Abstract

Introduction Despite the use of bismuth shields to reduce dose to eye lens and thyroid from CT scans has been reported efficient and recommended, there are conflicting opinions regarding breast bismuth shielding during thoracic CT. Purpose To assess breast dose reduction and diagnostic quality degradation associated with the use of bismuth shields in women undergoing coronary CT angiography (CCTA). Materials and methods Standard prospective and retrospective 256-slice CCTA exposures with and without breast bismuth shielding were simulated on a series of female anthropomorphic mathematical phantoms of varying size and 45 voxelized phantoms corresponding to patients subjected to CCTA using Monte Carlo methods. Bismuth shielding-induced reduction in dose to breast, lung and esophagus was determined. The effect of breast and thorax size on reduction efficiency was investigated. Shielding-related diagnostic quality degradation was assessed by two experienced radiologists in the series of 45 female patients subjected to CCTA. Results Breast bismuth shielding was found to reduce dose to breast, lung and esophagus of anthropomorphic phantoms by 22–33%, 12–21% and 13–20%, respectively. Corresponding mean reduction efficiency determined in voxelized phantoms of 45 CCTA patients was found 8–24%. The diagnostic quality degradation associated with the use of breast bismuth shields during CCTA was found to be unimportant. Conclusion Despite the breast dose reduction efficiency of bismuth shielding during CCTA was found lower than corresponding values reported in literature for thoracic CT, the use of breast bismuth shields in CCTA is not to be discouraged since associated diagnostic quality degradation is inconsequential.