Huang P H, Chu J, Bjärngard B E
Med Phys. 1987 Mar-Apr;14(2):268-9. doi: 10.1118/1.596137.
The field-size dependence of the photon output of linear accelerators in air has been attributed in part to changes in the amount of radiation backscattered from the collimator jaws into the dose monitor chamber. This possible effect was investigated for a variety of accelerators with energies from 4 to 15 MV by measuring the monitor unit rate (MU/min) for different collimator openings. This measurement was made without dose rate feedback control, i.e., with constant electron beam current in the accelerator. The monitor unit rate was independent of collimator setting for all machines tested. Hence, it is concluded that backscattered radiation from the collimator jaws into the dose monitor chamber does not contribute to the variation of output with field size.
直线加速器在空气中的光子输出对射野大小的依赖性，部分归因于从准直器钳口反向散射到剂量监测电离室中的辐射量的变化。通过测量不同准直器开口的监测单位率（MU/分钟），对各种能量在4至15MV之间的加速器研究了这种可能的影响。该测量是在没有剂量率反馈控制的情况下进行的，即在加速器中电子束电流恒定的情况下进行。对于所有测试的机器，监测单位率与准直器设置无关。因此，可以得出结论，从准直器钳口反向散射到剂量监测电离室中的辐射不会导致输出随射野大小而变化。
