Patterson M S, Shragge P C
Med Phys. 1981 May-Jun;8(3):312-8. doi: 10.1118/1.594833.
The 18 MV photon beam characteristics of a Therac 20 Medical Linear Accelerator manufactured by Atomic Energy of Canada Ltd, are presented. Tissue phantom ratios (TRP's) and percent depth dose data are given; for a 10 x 10 cm field, the percent depth dose at a depth of 10 cm is 78.5 (SSD 100 cm). The relative dose factors (RDF'S) are given and are analyzed to elucidate the relative contributions from phantom scatter, collimator scatter, and backscatter from the top of the collimators into the monitor chambers. The effect of field size and depth on the penumbra is described. Crossplots of the beam at a depth of 5 cm indicate that the flattening filter could be improved; there are hot spots of 108% near the corners of 40 x 40 fields.
介绍了加拿大原子能有限公司制造的Therac 20医用直线加速器的18 MV光子束特性。给出了组织体模比（TRP）和百分深度剂量数据；对于10×10 cm的射野，10 cm深度处的百分深度剂量为78.5（源皮距100 cm）。给出了相对剂量因子（RDF）并进行了分析，以阐明体模散射、准直器散射以及准直器顶部向监测电离室的反向散射的相对贡献。描述了射野大小和深度对半值层的影响。5 cm深度处射野的交叉图表明，均整滤过器可以改进；在40×40射野的角落附近存在108%的热点。
