CELL RADIATION RESPONSE AT LOW DOSE RATES

对于一般人群来说，生物活性物质造成的危害 在我们的环境中--或与健康服务相关的--预计将 这是由于长期服用低剂量药物所致。的危险。 主要关注的是那些与细胞失活、突变、 转化，并改变分化。估计…的程度 风险，通常认为影响遵循线性或 “一次击中”的剂量依赖性，其比率通常可以从 从高剂量辐射产生的效应外推到零剂量 高剂量率。与线性假设相关的是 隐含的假设，即效应的大小独立于 剂量传递率。这一假设来自于传统的 靶理论的应用，即单个吸收事件在 敏感的目标会产生这种效果。因此，次要有效 事件没有登记，因此，生化/生物过程 在曝光期间或在曝光之间不能改变影响的程度。然而， 通常应用的目标理论只是一种极限解 更一般的关系，根据该关系，如果仅 靶中吸收事件的(与剂量无关的)部分为 有效。因此，发生的生物化学/生物过程 在长时间暴露期间可能会改变以下事件的比例 也就是线性相关性的斜率。使用中文 仓鼠细胞在培养和终点对6-硫鸟嘌呤的抗性， X射线和伽马射线在高剂量率和低剂量率下的突变将是 以确定修复过程在低剂量下是否明显 区域。从长远来看，这项工作将扩大到包括其他 表型标记，到人类细胞，到其他物理以及 化学诱导剂。

For the population at large, the hazards due to biologically active agents in our environment--or associated with health services--are expected to result from low doses delivered over protracted periods. The hazards of main concern are those connected with cell inactivation, mutation, transformation, and altered differentiation. To estimate the degree of risk, it is customary to assume that the effect follows a linear or "single-hit" dose dependence whose rate may be inferred usually from an extrapolation to zero dose from effects produced by high doses delivered at high dose rates. Connected with the assumption of linearity is the implicit assumption that the magnitude of an effect is independent of the rate of dose delivery. This assumption comes from the conventional application of target theory, i.e., a single absorption event in the sensitive target produces the effect. As a consequence, sub-effective events are not registered and hence, biochemical/biological processes during or between exposures cannot modify the degree of effect. However, target theory as conventionally applied is only a limiting solution of a more general relationship according to which linearity also results if only a (dose-independent) fraction of the absorption events in the target is effective. Consequently bio-chemical/biological processes which occur during a protracted exposure may modify the proportion of events that are expressed and hence, the slope of the linear dependence. Using Chinese hamster cells in culture and the endpoint resistance to 6-thioguanine, mutations at high and at low dose rates by X- and Gamma-rays will be compared to determine if repair processes are evident in the low dose region. In the longer term, the work will be broadened to include other phenotypic markers, to human cells, and to other physical as well as to chemical inducers.