^(60)Co机准直器散射因子(Sc)的性质

Properties of collimator scatter factor (Sc) of cobalt60 unit

目的测量６０Ｃｏ机准直器散射因子（Ｓｃ）的性质，为临床使用提供依据。材料与方法在两种类型６０Ｃｏ机上，用指形电离室测量Ｓｃ随各种因素的变化规律。测量时，电离室的轴线与照射野的射线束轴重合。结果获得了Ｓｃ与源皮距的关系数据。分析了不同矩形野Ｓｃ的变化，挡块对Ｓｃ影响等。结论在一般照射野大小，Ｓｃ与源皮距无关，并可用二次函数来拟合Ｓｃ随照射野大小的变化。挡块及有机玻璃托盘对Ｓｃ影响可忽略。但在大野时Ｓｃ略有不同。

Purpose The properties of collimator scatter factor (Sc) was measured in order to form the basis of clinical usage.Materials and Methods The effects of various factors to Sc was measured by dosimeter NE2560 and NE2620 on the 780C and C9 cobalt60 units. The axis of ionization chamber was aligned along the center axis of field in the experimental process.Results The data of the relationship between Sc and SSD was obtained. The variation of Sc according to the rectangle field and block were analyzed.Conclusion When the fields are in the general size, Sc is independent from SSD and the relation of them can conform to quadratic function. The effect of the block and tray can be ignored. However, in the large size condition the properties are somewhat different. The special effective field equation of rectangle field is supposed in this paper according the experimental result.