Radiology: Volume 260: Number 2-August 2011
Leslie C. Chatterson, MD David A. Leswick, MD, FRCPC Derek A. Fladeland, MD, FRCPC Megan M. Hunt, BE, MSc Stephen T. Webster, BSc, MSc
Purpose: To compare the effective fetal dose reduction at differ¬ent stages of gestation during maternal computed tomo¬graphic (CT) pulmonary angiography by using traditional lead apron and bismuth-antimony shields combined with limited z-axis and tube current.
Methods and Materials: Phantom with gravid prosthesis, 0.5-mm lead, and two grades of bismuth-antimony shield was used. Thermolu-minescent dosimeters (TLDs) measured radiation in the first- to third-trimester uterus. Fetal dose was determined for each gestation by using 100 kVp to the costophrenic angles (CPAs) with and without shielding for a total of 12 scans. Eight third-trimester scans were used to com¬pare shields using 120 kVp to CPAs versus those using 100 kVp to the diaphragm.
Results: Average fetal dose increased with gestation with use of 100 kVp to CPAs, from 0.11 mGy in first trimester to 0.50 mGy in third trimester. Average third-trimester unshielded fetal dose was reduced from 0.82 mGy by using 120 kVp to CPAs to 0.17 mGy (79%, P < .001) by using 100 kVp to the diaphragm. Lead apron reduced dose more than ei¬ther of the bismuth-antimony shields (72%-79% vs 57%-81%) with use of 100 kVp to CPAs. Shields reduced the dose by 73% (lead), 62% (90% attenuation bismuth-antimony), and 72% (95% attenuation bismuth-antimony) (P < .01) at 120 kVp to CPAs. No significant difference between shields was demonstrated with 100 kVp to the diaphragm (P < .01). Maternal dose was 8.13 mSv at 120 kVp to CPAs, 4.90 mSv at 100 kVp to CPAs, and 4.02 mSv at 100 kVp to the diaphragm.
Conclusion: Reducing voltage and limiting z-axis is more effective than shields at reducing fetal dose. Shielding improves reduction with no significant difference between lead and bismuth-antimony shields when conservative scanning parameters are observed.