Uncertainties due to confounding factors in epidemiological studies have limited our knowledge of the effects of low-dose-rate chronic exposure on human health. Animal experiments, wherein each subject is considered to be nearly identical, can complement the limitations of epidemiological studies. Therefore, we conducted a joint analysis of previously published cancer mortality data in B6C3F1 female mice chronically and acutely irradiated with ¹³⁷Cs γ rays to estimate the dose-rate effectiveness factor. In the chronically irradiated animal experiment conducted by the Institute for Environmental Sciences, mice received irradiation at dose rates of 0.05, 1.1 or 21 mGy per day for 400 days from 8 weeks of age. For the acutely irradiated animal experiment conducted by the National Institute of Radiological Sciences, mice received irradiation at 35, 105, 240 or 365 days of age with 1.9, 3.8 or 5.9 Gy at a dose rate of 0.98 Gy per min. Because the preliminary analyses suggested that the risk was dependent on the age at exposure, a model was applied that considered risk differences depending on this factor. The model analysis revealed a three-fold, significantly decreased risk per Gy in mice exposed to 21 mGy per day compared to that in acutely irradiated mice. This resulted in a dose-rate effectiveness factor larger than that reported previously.

由于流行病学研究中混杂因素造成的不确定性限制了我们对低剂量率长期暴露对人体健康的影响的了解。在动物实验中，每个受试者被认为几乎是相同的，可以弥补流行病学研究的局限性。因此，我们对长期和急性照射B6C3F1雌性小鼠的^137例先前发表的癌症死亡率数据进行了联合分析。用Csγ射线估计剂量率有效因子。在环境科学研究所进行的长期辐照动物实验中，小鼠从8周龄开始以每天0.05、1.1或21 mGy的剂量率接受辐照，持续400天。对于由国家放射科学研究院进行的急性辐照动物实验，小鼠在35、105、240或365天龄时接受了1.9、3.8或5.9 Gy的辐照，辐照速率为每分钟0.98 Gy。由于初步分析表明风险取决于暴露年龄，因此应用了一个模型，该模型根据此因素考虑了风险差异。模型分析显示，每天暴露于21 mGy的小鼠与急性照射的小鼠相比，每Gy的风险显着降低了三倍。