垂直偏波遠方界ばく露の妊婦・胎児と乳幼児に対する全身平均SARの統計解析

摘要

In 2006, WHO (World Health Organization) recommended the necessity of dosimetry evaluation for children and pregnant women with fetus as one of most primary research subjects, which has promoted the studies on whole-body-average specific absorption rates (WBA-SARs) in various kinds of numerical child models with respect to safety limits of WBA-SARs. For the present safety limits, however, they are being determined based on the behavior destruction of healthy adult animals for radio-frequency exposure, which are not being obtained for young or pregnant animals. Because of this reason, we think that it is necessary to study more absorption property in pregnant woman with fetus and infant for electromagnetic wave exposure. In this study, we calculated the WBA-SARs in anatomical models for pregnant woman with fetus and 3 years child, and statistically analyzed the voxel SARs at resonant frequencies. As a result, we found that the mean of the voxel SARs approximately agree with the WBA-SARs, and that the medians of the pregnant woman and 3-years child models are about 47 % and 55 %, respectively, smaller than their means. It was also found that the total number ratio of voxel SARs exceeding 99.7 % value of log-normal distribution or normal distribution is 0.41 % for the pregnant woman model, 0.39 % for the 3-years child model and 1.0 % for the fetus model. The finding implies that the FDTD method is likely to overestimate WBA-SARs due to the presence of voxel SARs with extreme values.%乳幼児や妊婦・胎児への電波ばく露に対する影響の関心が高まり，全身平均SARの数値解析が広く行われている．そもそも全身平均SARの閥値は，健康な小動物を用いた電波ばく露実験により誘発される行動分裂とその共振特性を基に定められたものであり，幼若動物や妊娠動物を対象とした実験に基づくものでない．それ故に，小児や妊娠女性・胎児の電波吸収特性に対しては，全身平均SAR値だけでなく，体内の空間吸収分布と併せて，更なる検討が必要であると筆者らは考える．本稿では，垂直偏波の遠方界ばく露で生ずる妊娠女性と3歳児モデルの全身平均SARをFDTD法で計算し，全身平均SARが最大となる共振周波数でのボクセルSARの統計解析を行った．その結果，ボクセルSARの平均値は全身平均SAR値にほぼ一致すること，平均値に対し中央値は大幅に下回り，妊娠女性では約47％，3歳児では約55％であること，妊娠女性と3歳児のボクセルSARは対数正規分布に大略当てはまること，異常値を示すボクセルは妊娠女性では0.41％，3歳児では0.39％であったこと，胎児のボクセルSARは正規分布にほぼ当てはまり，ボクセル異常値の割合は1.0％であったこと，などがわかった．