Kubo H, Lo K K
Department of Radiation Oncology, University of Rochester Cancer Center, New York 14642.
Med Phys. 1989 Mar-Apr;16(2):292-4. doi: 10.1118/1.596380.
The field size dependent photon output is known to be influenced by the existence of backscattered radiation (BSR) generated in the collimator or trimmer jaws of a linear accelerator. This paper describes the results of measurements made to study the existence of such backscatter by simulating the geometry of the treatment head of a Therac-20 linear accelerator. The machine's monitor chamber, flattening filter, and collimator jaws were simulated by another real monitor chamber, a 1-cm thick lead sheet and 2.5-cm thick low-melting-point alloy divergent blocks, respectively. BSR from the simulated collimator jaws (SCJ) was measured with the simulated monitor chamber (SMC) as a function of the openings of the SCJ and as a function of distance between SMC and SCJ. The present results demonstrate the presence of BSR in an 18-MV photon beam from a Therac-20 linear accelerator.
已知取决于射野大小的光子输出会受到直线加速器准直器或限束器钳口中产生的反向散射辐射（BSR）的影响。本文描述了通过模拟Therac - 20直线加速器治疗头的几何结构来研究此类反向散射存在情况的测量结果。该机器的监测电离室、均整器和准直器钳口分别由另一个实际监测电离室、一块1厘米厚的铅板和2.5厘米厚的低熔点合金发散块模拟。用模拟监测电离室（SMC）测量来自模拟准直器钳口（SCJ）的BSR，作为SCJ开口的函数以及SMC与SCJ之间距离的函数。目前的结果证明了Therac - 20直线加速器的18兆伏光子束中存在BSR。
