Zrenner M, Krieger H
Klinikum Ingolstadt.
Strahlenther Onkol. 1999 Oct;175(10):515-23. doi: 10.1007/s000660050063.
Modern linear accelerators permit the use of irregular fields due to their flexible collimator systems with separately movable jaws or multileaf collimators. When using such irregular fields in the clinical practice output factors have to be corrected for enhanced backscatter to the dose monitor as compared with the conventional block shieldings.
A method is presented to detect the monitor backscatter contributions to the output factor for irregular field settings.
The monitor backscatter factors have been measured using a telescopic device for 2 different treatment head geometries (Varian Clinac 2100C/D, General Electric Saturne 15) and for 3 photon radiation qualities (nominal energies X6, X18, X12). A method is introduced to calculate the monitor backscatter for arbitrary irregular treatment fields from the experimental data for square or rectangular fields.
Besides the corrections for changes in phantom scatter and changes in the aperture, corrections for monitor backscatter have to be taken into account in many clinical cases. They can contribute up to more than 10% compared with the monitor values for free regular fields.
现代直线加速器由于其具有可单独移动准直器或多叶准直器的灵活准直器系统，允许使用不规则射野。在临床实践中使用此类不规则射野时，与传统挡块屏蔽相比，必须针对剂量监测器增强的反向散射对输出因子进行校正。
提出了一种检测监测器反向散射对不规则射野设置输出因子贡献的方法。
使用伸缩装置针对2种不同治疗头几何形状（瓦里安Clinac 2100C/D、通用电气Saturne 15）以及3种光子辐射质（标称能量X6、X18、X12）测量了监测器反向散射因子。引入了一种方法，可根据方形或矩形射野的实验数据计算任意不规则治疗射野的监测器反向散射。
除了对模体散射变化和射野孔径变化进行校正外，在许多临床病例中还必须考虑对监测器反向散射的校正。与自由规则射野的监测器值相比，它们的贡献可达10%以上。
