Little M P
Radiation Epidemiology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-9778, USA.
Ann ICRP. 2018 Oct;47(3-4):97-112. doi: 10.1177/0146645318756235. Epub 2018 Apr 13.
For stochastic effects such as cancer, linear-quadratic models of dose are often used to extrapolate from the experience of the Japanese atomic bomb survivors to estimate risks from low doses and low dose rates. The low dose extrapolation factor (LDEF), which consists of the ratio of the low dose slope (as derived via fitting a linear-quadratic model) to the slope of the straight line fitted to a specific dose range, is used to derive the degree of overestimation (if LDEF > 1) or underestimation (if LDEF < 1) of low dose risk by linear extrapolation from effects at higher doses. Likewise, a dose rate extrapolation factor (DREF) can be defined, consisting of the ratio of the low dose slopes at high and low dose rates. This paper reviews a variety of human and animal data for cancer and non-cancer endpoints to assess evidence for curvature in the dose response (i.e. LDEF) and modifications of the dose response by dose rate (i.e. DREF). The JANUS mouse data imply that LDEF is approximately 0.2-0.8 and DREF is approximately 1.2-2.3 for many tumours following gamma exposure, with corresponding figures of approximately 0.1-0.9 and 0.0-0.2 following neutron exposure. This paper also cursorily reviews human data which allow direct estimates of low dose and low dose rate risk.
对于诸如癌症等随机效应，剂量的线性二次模型常被用于从日本原子弹幸存者的经验进行外推，以估计低剂量和低剂量率下的风险。低剂量外推因子（LDEF）由低剂量斜率（通过拟合线性二次模型得出）与拟合特定剂量范围的直线斜率之比组成，用于得出通过从较高剂量效应进行线性外推对低剂量风险的高估程度（如果LDEF > 1）或低估程度（如果LDEF < 1）。同样，可以定义剂量率外推因子（DREF），它由高剂量率和低剂量率下的低剂量斜率之比组成。本文综述了关于癌症和非癌症终点的各种人类和动物数据，以评估剂量反应曲线弯曲（即LDEF）和剂量率对剂量反应的修正（即DREF）的证据。JANUS小鼠数据表明，对于许多γ射线照射后的肿瘤，LDEF约为0.2 - 0.8，DREF约为1.2 - 2.3，而中子照射后的相应数字约为0.1 - 0.9和0.0 - 0.2。本文还简要综述了可直接估计低剂量和低剂量率风险的人类数据。
