Yu M K, Sloboda R S
Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
Int J Radiat Oncol Biol Phys. 1997 Jan 15;37(2):465-8. doi: 10.1016/s0360-3016(96)00495-6.
This study aimed to investigate the influence of beam blocking on head scatter within the context of a two-component x-ray source model.
Head scatter factors were measured for open rectangular fields defined by X and Y jaws and for fields blocked by a multileaf collimator (MLC) for a 6-MV photon beam from a Varian 2300CD accelerator. A simple formula based on consideration of linac head geometry and an x-ray source model was derived to determine when the head scatter factor for a shaped field depends only on jaw settings and when it is influenced by the blocking (cerrobend blocks or MLC) itself.
Experimental data demonstrate that the assumption that head scatter is unaffected by the introduction of beam blocking is not always acceptable, particularly for fields blocked by an MLC. The ratios of open to blocked field dimensions were compared with simple functions characterizing the accelerator head geometry to predict changes in the behavior of head scatter factors observed experimentally.
A simple formula can be used to determine when head scatter factors are influenced by beam blocking (cerrobend blocks or MLC).
本研究旨在探讨在双组分X射线源模型的背景下，射束遮挡对头部散射的影响。
对瓦里安2300CD加速器产生的6兆伏光子束，测量由X和Y光阑定义的开放矩形野以及由多叶准直器（MLC）遮挡的野的头部散射因子。基于对直线加速器头部几何形状和X射线源模型的考虑，推导了一个简单公式，以确定成形野的头部散射因子何时仅取决于光阑设置，何时受遮挡物（铈钨合金挡块或MLC）本身的影响。
实验数据表明，射束遮挡的引入不会影响头部散射这一假设并非总是成立，特别是对于由MLC遮挡的野。将开放野与遮挡野的尺寸比与表征加速器头部几何形状的简单函数进行比较，以预测实验观察到的头部散射因子行为的变化。
可使用一个简单公式来确定头部散射因子何时受射束遮挡（铈钨合金挡块或MLC）的影响。
