Kalpana M. Kanal PhD, Presenter: Nothing to Disclose

Martin Lee David Gunn MBChB, Abstract Co-Author: Nothing to Disclose

William Phelps Shuman MD, Abstract Co-Author: Research grant, General Electric Company, Milwaukee, WI

Orpheus Kolokythas MD, Abstract Co-Author: Consultant, Koninklijke Philips Electronics NV Investigator, Koninklijke Philips Electronics NV Research grant, Koninklijke Philips Electronics NV

To determine the degree of breast dose reduction when bismuth breast shields are applied concurrently with automated tube current modulation on a 64 channel CT scanner.

An anthropomorphic phantom was scanned using a commercially available 64 channel CT scanner. Standardized CT pulmonary angiography and abdominal protocols were used with automated tube current modulation. A prospectively gated CT coronary artery angiography protocol without tube current modulation was also acquired. Scans were performed without and with a bismuth breast shield. The bismuth breast shields were applied between scouts and helical or axial acquisitions, except for one series when the shield was applied prior to the scout. Therumoluminscent dosimeters were placed on surface and deep within the breasts for each scan. A paired t-test and 95% confidence intervals were used to determine whether the skin entry dose and approximate mean glandular dose differed significantly following the use of bismuth shielding.

There was significant breast dose reduction for all protocols when an inline bismuth impregnated breast shield was applied. For CT pulmonary angiography, deep breast dose was reduced by 46.0%, from 14.7 mGy (CI 0.05 13.2– 16.2 mGy) without shielding to 7.9 mGy (CI 0.05 7.5 – 8.3) following shielding (p<0.0001). When a shield is applied prior to the scout (AP then lateral scout order), the dose reduction is smaller at 25.4% (p<0.001). When breast shields are applied prior to abdominal CT, there is a 35% deep breast dose reduction (p=0.001). When prospective cardiac gating is used combined with bismuth shielding, but without tube current modulation, there is a 83.8% skin entry exposure reduction (p<0.000001).

Significant breast dose reduction is achieved by using a combination of automated tube current modulation and bismuth shielding. In systems where tube current modulation is determined by the scout series, the bismuth shield is most effective when the shield is applied between the scout and the helical or axial acquisition. Breast shield, in combination with prospective cardiac gating, can result in significant breast dose savings.  

Bismuth shielding is an effective means of reducing breast radiation dose when combined with tube current modulation, and can potentially reduce the risk of radiation induced breast cancer.

Kanal, K, Gunn, M, Shuman, W, Kolokythas, O, Bismuth Breast Shielding with Adaptive Tube Current Modulation: Is Breast Dose Significantly Reduced?.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6019587.html