(Wednesday, 8/1/2018) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 1
Purpose: Bismuth breast shields and global mAs reduction are both tools to reduce breast organ dose. However, in pediatric CT of chest, abdomen, and pelvis (CAP protocols), globally reducing mAs is detrimental to abdominal image quality. The purpose of this work is to compare breast dose reduction with bismuth shields to the use of global mAs reduction utilizing a region-specific boost feature to maintain abdominal image quality.
Methods: Three phantoms (WED 16.6, 23.5, 28.9 cm) were scanned under two conditions: with a breast shield, and with globally reducing mAs to match the noise level at heart (with a breast shield). Scan parameters were adjusted, utilizing the liver region boost feature, to match noise levels in the heart and liver. Entrance skin exposures were measured at the anterior and posterior surfaces for comparison. Image quality was assessed using standard deviation measurements in the heart and liver regions.
Results: In the largest phantom, global dose reduction strategies produced the same dose savings previously seen while using a bismuth shield at the breast entrance. Additionally, the posterior entrance skin exposure was reduced by 16%. In the medium phantom, global dose reduction strategies resulted in modest breast dose penalties, but demonstrated a 17% dose saving at the posterior surface. A steady mAs gradient, resulting from the applied boost, contributed to the loss of breast dose savings. This gradient made application of the boost feature detrimental in the smallest phantom, presenting patient sizes for which breast shields should be used.
Conclusion: For pediatric CT CAP studies performed on patients less than 23.5 cm, the method of global mAs reduction with the boost feature was less effective in breast dose reduction than the bismuth shield. In pediatric patients larger than 23.5 cm, the global mAs reduction method with boost can be employed making breast shields unnecessary.
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