National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan.
University of Tokyo, Chiba, Japan.
Health Phys. 2020 Jan;118(1):36-52. doi: 10.1097/HP.0000000000001125.
The dose reconstruction of populations potentially affected by the accident at the Fukushima Daiichi nuclear power plant in March 2011 is of great importance. However, it has been difficult to assess internal thyroid doses to Fukushima residents (mainly from their intake of I) due to the lack of direct measurements. For the residents, only about 1,300 data points related to I are available, and 1,080 of the data points were obtained from the screening campaign that was conducted by the Nuclear Emergency Response Local Headquarters at the end of March 2011 in Kawamata Town, Iwaki City, and Iitate Village. Here, we reassessed thyroid doses to 1,080 subjects aged ≤15 y old using new age-specific conversion factors to determine I thyroid contents from net signals of the devices used, with consideration for the possible uncertainty related to the measurements. The results demonstrated that thyroid equivalent doses to the subjects were <30 mSv (excluding outliers). We also demonstrate dose distributions of each age group from the above three municipalities and those of subjects from Minamisoma City and Fukushima City. One of the findings was that the I intake was similar among different age groups in each of the three municipalities. This was consistent with the assumption that ingestion was a dominant route of intake rather than inhalation. The range of thyroid doses to Iitate Village residents was similar to that to Iwaki City residents even though the I concentration in tap water was much higher in Iitate Village than Iwaki City. The range of thyroid doses to Minamisoma City residents was similar to that to Iitate Village and Iwaki City residents, and the range for Fukushima City residents was smallest among the five municipalities. Since the major route of intake has remained unclear, this paper presents the plausible upper and lower thyroid doses, between which the actual doses are thought to mostly exist, based on two intake scenarios: single inhalation and repeated ingestion. Further research is thus necessary to extract useful evidence from the individual evacuation behaviors for improving the present internal thyroid dose assessment.
对 2011 年 3 月福岛第一核电站事故中受影响人群进行剂量重建非常重要。然而，由于缺乏直接测量，评估福岛居民（主要通过摄入碘）的体内甲状腺剂量一直很困难。对于居民来说，只有大约 1300 个与碘相关的数据点，其中 1080 个数据点是 2011 年 3 月底在岩城市川内町和伊庭村由核应急响应地方总部进行的筛查活动获得的。在这里，我们使用新的年龄特异性转换因子重新评估了 1080 名年龄≤15 岁的受试者的甲状腺剂量，以确定从设备的净信号中得出的碘甲状腺含量，并考虑到与测量相关的可能不确定性。结果表明，受试者的甲状腺当量剂量<30mSv（不计异常值）。我们还展示了上述三个市町村每个年龄组的剂量分布以及来自相马市和福岛市的受试者的剂量分布。一个发现是，在这三个市町村的每个年龄组中，碘的摄入量都相似。这与摄入是主要摄入途径而不是吸入的假设一致。伊庭村居民的碘摄入量与岩城市居民相似，尽管伊庭村自来水中的碘浓度远高于岩城市。相马市和岩城市居民的甲状腺剂量范围相似，而福岛市居民的甲状腺剂量范围在五个市町村中最小。由于主要摄入途径仍不清楚，本文根据两种摄入情景（单次吸入和多次摄入）提出了可能的上下限甲状腺剂量，实际剂量被认为主要存在于这两个剂量之间。因此，需要进一步研究从个体疏散行为中提取有用证据，以改进目前的内部甲状腺剂量评估。
