Miyazaki Osamu, Sawai Hideaki, Yamada Takahiro, Murotsuki Jun, Nishimura Gen
1 Department of Radiology, National Center for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo 157-8535, Japan.
2 Department of Obstetrics and Gynecology, Hyogo College of Medicine, Hyogo, Japan.
AJR Am J Roentgenol. 2017 Apr;208(4):862-867. doi: 10.2214/AJR.16.17316.
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.
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 (CTDI), dose-length product (DLP), and scan length of 120 fetal CT examinations. The trends for IR usage and tube voltage were also investigated.
Compared to the results of the 2011 study (n = 119), the minimum, 25th percentile, median, and 75th percentile values for CTDI and DLP have decreased for the tabulated results in 2015 (n = 120). The 75th percentile value for CTDI 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.
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.
2011年，我们收集了胎儿CT辐射剂量数据以确定诊断参考水平（DRL）；然而，对DRL进行持续评估是必要的。本研究的假设是胎儿CT辐射剂量已降低，并且我们预测迭代重建（IR）将得到广泛应用。我们还预测全国范围内辐射剂量的降低是由于先前全国性研究报告的DRL。
作为研究结果的一部分，总结了各站点的各种测试方案。获取了120例胎儿CT检查的容积CT剂量指数（CTDI）、剂量长度乘积（DLP）和扫描长度的最小值、四分之一值（第25百分位数）、中位数、四分之三值（第75百分位数）和最大值。还调查了IR使用情况和管电压的趋势。
与2011年研究结果（n = 119）相比，2015年列表结果（n = 120）中CTDI和DLP的最小值、第25百分位数、中位数和第75百分位数均有所降低。CTDI的第75百分位数为4.9 mGy，是先前值的43%。70%的站点使用了IR。使用IR的组辐射剂量显著更低。
从我们最初关于DRL的调查到本次随访调查过去了四年，先前的报告似乎充分实现了其目标，并在促成本次随访研究中观察到的DRL降低方面发挥了作用。
