Klevenhagen S C, Lambert G D, Arbabi A
Phys Med Biol. 1982 Mar;27(3):363-73. doi: 10.1088/0031-9155/27/3/003.
Whenever a heterogeneity is present in an electron beam treatment field during radiotherapy, there is the possibility of tissue overdosage at the tissue-heterogeneity interface due to electrons backscattered from the heterogeneity. Measurements of this effect were made in a polystyrene phantom using a purpose-built thin-window parallel-plane ionisation chamber. Materials of various atomic numbers were used as scatterers and the investigations were made over a wide range of electron energies. Electron backscatter factor (EBF), defined as the ratio fo dose at the interface surface with and without the scatterer present, was found to increase with increasing atomic number and decrease with increasing beam energy. Both of these relationships were found to be non-linear. The EBF dependence on the scatterer thickness was also investigated. All data in this work were expressed in relation to the beam energy incident on the scatterer in preference to the nominal beam energy set on the accelerator. This approach enables the dose enhancement at an interface to be predicted from a knowledge of the heterogeneity (atomic number and thickness,), its depth in tissue and the beam energy being used for treatment. The results of this work were compared with the published data and an explanation is offered to account for the difference.
在放射治疗期间，当电子束治疗野中存在不均匀性时，由于从不均匀性反向散射的电子，在组织 - 不均匀性界面处存在组织过量照射的可能性。使用特制的薄窗平行板电离室在聚苯乙烯模体中对这种效应进行了测量。使用各种原子序数的材料作为散射体，并在很宽的电子能量范围内进行了研究。电子反向散射因子（EBF）定义为存在和不存在散射体时界面表面剂量之比，发现其随原子序数增加而增加，随束流能量增加而降低。发现这两种关系都是非线性的。还研究了EBF对散射体厚度的依赖性。这项工作中的所有数据均表示为相对于入射到散射体上的束流能量，而不是加速器上设置的标称束流能量。这种方法能够根据对不均匀性（原子序数和厚度）、其在组织中的深度以及用于治疗的束流能量的了解来预测界面处的剂量增强。将这项工作的结果与已发表的数据进行了比较，并对差异给出了解释。
