Redpath J Leslie
Department of Radiation Oncology, University of California Irvine, Irvine, CA.
Nonlinearity Biol Toxicol Med. 2005 Jan;3(1):113-24. doi: 10.2201/nonlin.003.01.007.
There are now several independent studies that indicate that the dose-response for the endpoint of radiation-induced neoplastic transformation in vitro is non-linear for low linear energy transfer (LET) radiation. At low doses (<10 cGy) the transformation frequency drops below that seen spontaneously. Importantly, this observation has been made using fluoroscopic energy x-rays, a commonly used modality in diagnostic radiology, the practice of which is responsible for the majority of radiation exposure to the general public. Since the transformation frequency is reduced over a large dose range (0.1 to 10cGy) it is likely that multiple mechanisms are involved and that the relative contribution of these may vary with dose. These include the killing of a subpopulation of cells prone to spontaneous transformation at the lowest doses, and the induction of DNA repair at somewhat higher doses. Protective effects of low doses of low LET radiation on other cancer-relevant endpoints in vitro and in vivo have also been observed by several independent laboratories. These observations strongly suggest that the linear-nonthreshold dose-response model is unlikely to apply to the induction of cancer by low doses of low LET radiation in humans.
现在有几项独立研究表明，对于低线性能量传递（LET）辐射，体外辐射诱导肿瘤转化终点的剂量反应是非线性的。在低剂量（<10 cGy）时，转化频率低于自发出现的频率。重要的是，这一观察结果是使用荧光透视能量X射线得出的，荧光透视能量X射线是诊断放射学中常用的一种方式，而这种方式导致了普通公众大部分的辐射暴露。由于在较大剂量范围（0.1至10 cGy）内转化频率降低，可能涉及多种机制，并且这些机制的相对贡献可能随剂量而变化。这些机制包括在最低剂量时杀死易于自发转化的细胞亚群，以及在稍高剂量时诱导DNA修复。几个独立实验室还观察到低剂量低LET辐射在体外和体内对其他癌症相关终点的保护作用。这些观察结果强烈表明，线性无阈剂量反应模型不太可能适用于低剂量低LET辐射对人类癌症的诱导。
