Department of Radiation Oncology, University of California Irvine, Irvine, CA, USA.
Dose Response. 2006 Dec 6;5(2):123-30. doi: 10.2203/dose-response.06-010.Redpath.
Dose-response curves for various low-LET radiation sources have consistently been demonstrated to be J-shaped for the cancer-relevant endpoint of neoplastic transformation in vitro. Most of these studies have been performed where the radiation has been delivered at intermediate to high dose-rates (30-3000 mGy/min), where the threshold dose for induction of neoplastic transformation is around 100-200 mGy. Below these doses, the transformation frequency is less than that seen spontaneously, indicative of a hormetic effect. More recently, data have been obtained for low dose rates (<0.5 mGy/min) of low-LET radiation, and again hormetic effects are apparent but with threshold doses now being >1000 mGy. Similar trends have been reported in animal experiments as well as in human epidemiologic studies. Indeed, the relative risks for induction of neoplastic transformation in vitro in the dose range 1 to 1000 mGy agree well with those for incidence of radiation-induced breast cancer and leukemia in humans. These findings support the notion that the endpoint of neoplastic transformation in vitro is a plausible endpoint to not only study mechanisms involved in response to low doses of radiation, but also to provide information of potential importance to risk assessment.
各种低 LET 辐射源的剂量反应曲线对于体外肿瘤转化这一癌症相关终点一直表现为 J 形。这些研究大多数是在中等至高剂量率（30-3000 mGy/min）下进行的，其中诱导肿瘤转化的起始剂量约为 100-200 mGy。在这些剂量以下，转化频率低于自发转化频率，表明存在兴奋效应。最近，已经获得了低 LET 辐射低剂量率（<0.5 mGy/min）的数据，同样明显存在兴奋效应，但起始剂量现在超过 1000 mGy。动物实验和人类流行病学研究也报告了类似的趋势。事实上，体外肿瘤转化的相对风险在 1 至 1000 mGy 的剂量范围内与人类因辐射引起的乳腺癌和白血病的发生率非常吻合。这些发现支持了这样一种观点，即体外肿瘤转化的终点不仅是研究低剂量辐射反应机制的合理终点，而且还为风险评估提供了潜在重要信息。
