Fetal shielding combined with state of the art CT dose reduction strategies during maternal chest CT.
OBJECTIVE
Custom bismuth-antimony shields were previously shown to reduce fetal dose by 53% on an 8DR (detector row) CT scanner without dynamic adaptive section collimation (DASC), automatic tube current modulation (ATCM) or adaptive statistical iterative reconstruction (ASiR). The purpose of this study is to compare the effective maternal and average fetal organ dose reduction both with and without bismuth-antimony shields on a 64DR CT scanner using DASC, ATCM and ASiR during maternal CTPA.


METHODS
A phantom with gravid prosthesis and a bismuth-antimony shield were used. Thermoluminescent dosimeters (TLDs) measured fetal radiation dose. The average fetal organ dose and effective maternal dose were determined using 100 kVp, scanning from the lung apices to the diaphragm utilizing DASC, ATCM and ASiR on a 64DR CT scanner with and without shielding in the first and third trimester. Isolated assessment of DASC was done via comparing a new 8DR scan without DASC to a similar scan on the 64DR with DASC.


RESULTS
Average third trimester unshielded fetal dose was reduced from 0.22 mGy ± 0.02 on the 8DR to 0.13 mGy ± 0.03 with the conservative 64DR protocol that included 30% ASiR, DASC and ATCM (42% reduction, P<0.01). Use of a shield further reduced average third trimester fetal dose to 0.04 mGy ± 0.01 (69% reduction, P<0.01). The average fetal organ dose reduction attributable to DASC alone was modest (6% reduction from 0.17 mGy ± 0.02 to 0.16 mGy ± 0.02, P=0.014). First trimester fetal organ dose on the 8DR protocol was 0.07 mGy ± 0.03. This was reduced to 0.05 mGy ± 0.03 on the 64DR protocol without shielding (30% reduction, P=0.009). Shields further reduced this dose to below accurately detectable levels. Effective maternal dose was reduced from 4.0 mSv on the 8DR to 2.5 mSv on the 64DR scanner using the conservative protocol (38% dose reduction).


CONCLUSIONS
ASiR, ATCM and DASC combined significantly reduce effective maternal and fetal organ dose during CTPA. Shields continue to be an effective means of fetal dose reduction.
Department of Diagnostic Imaging, University of Saskatchewan, Canada. Electronic address: lch088@mail.usask.ca.
Leslie C
LC
Chatterson
Department of Diagnostic Imaging, University of Saskatchewan, Canada.
David A
DA
Leswick
Department of Diagnostic Imaging, University of Saskatchewan, Canada.
Derek A
DA
Fladeland
Saskatchewan Ministry of Labour Relations and Workplace Safety, Canada.
Megan M
MM
Hunt
Saskatchewan Ministry of Labour Relations and Workplace Safety, Canada.
Stephen
S
Webster
Department of Community Health and Epidemiology, College of Medicine, University of Saskatchewan, Canada.
Hyun
H
Lim
D065638:Absorption, Radiation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D005333:Fetus / Q000000981:diagnostic imaging / Q000528:radiation effects*; D006801:Humans; D018811:Maternal Exposure / Q000517:prevention & control*; D019047:Phantoms, Imaging; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000295:instrumentation* / Q000379:methods; D011829:Radiation Dosage; D011835:Radiation Protection / Q000295:instrumentation*; D013902:Radiography, Thoracic / Q000295:instrumentation* / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods; D014915:Whole-Body Counting
ASiR; ATCM; DASC; Fetal dose reduction; Maternal CTPA; Shielding; Thoracic