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.

MATERIALS AND 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 CTDIvol and DLP have decreased for the tabulated results in 2015 (n = 120). The 75th percentile value for CTDIvol was 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.

CONCLUSION: 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.