Follow-Up Study on Fetal CT Radiation Dose in Japan: Validating the Decrease in Radiation Dose.
OBJECTIVE
In 2011, we collected data on fetal CT radiation dose to determine the diagnostic reference level (DRL); however, continuous evaluation of the DRL is necessary. The hypothesis of this study is that the fetal CT radiation dose has decreased, and we predict a widespread use of iterative reconstruction (IR). We also predict that the national decrease in exposure is because of the DRL reported as a result of the previous national study.


METHODS
Various testing protocols from each site were summarized as part of the study results. The minimum, one-fourth (25th percentile), median, three-fourths (75th percentile), and maximum values were obtained for volume CT dose index (CTDIvol), dose-length product (DLP), and scan length of 120 fetal CT examinations. The trends for IR usage and tube voltage were also investigated.


RESULTS
Compared to the results of the 2011 study (n = 119), the minimum, 25th percentile, median, and 75th percentile values for CTDIvoland DLP have decreased for the tabulated results in 2015 (n = 120). The 75th percentile value for CTDIvolwas 4.9 mGy, which is 43% of the previous value. IR was used in 70% of the sites. The radiation dose was significantly lower among groups that used IR.


CONCLUSIONS
Four years passed between our initial survey on DRL and the present follow-up survey, and it appears that the previous report sufficiently fulfilled its objective and role in contributing to the decrease in DRL observed in this follow-up study.
1 Department of Radiology, National Center for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo 157-8535, Japan.
Osamu
O
Miyazaki
2 Department of Obstetrics and Gynecology, Hyogo College of Medicine, Hyogo, Japan.
Hideaki
H
Sawai
3 Department of Obstetrics and Gynecology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Takahiro
T
Yamada
4 Department of Maternal and Fetal Medicine, Miyagi Children's Hospital, Miyagi, Japan.|5 Department of Advanced Fetal and Developmental Medicine, Tohoku University Graduate School of Medicine, Miyagi, Japan.
Jun
J
Murotsuki
6 Department of Pediatric Imaging, Tokyo Metropolitan Children's Medical Center, Tokyo, Japan.
Gen
G
Nishimura
D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D011296:Prenatal Diagnosis / Q000706:statistics & numerical data* / Q000639:trends; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000517:prevention & control* / Q000706:statistics & numerical data*; D011835:Radiation Protection / Q000706:statistics & numerical data*; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data* / Q000639:trends
CT; diagnostic reference level; fetus; prenatal diagnosis; skeletal dysplasia