PMMA与铜平衡帽对6MV光子线反散射因子和准直器散射因子测量结果影响的比较研究

目的:通过比较聚甲基丙烯酸甲酯(PMMA)与铜平衡帽对6 MV光子线反散射因子(BSF)和准直器散射因子(Sc)测量结果的影响,提出一种简单易行的测量高能光子线BSF和Sc的方法。材料与方法:分别使用PMMA与铜制平衡帽在SAD和SSD两种方式下测量6MV光子线的BSF和Sc,并比较分析测量数据。结果:相同条件下铜制平衡帽的吸收剂量值测量结果明显偏大,而Sc的数值与变化趋势在不同的平衡帽材料和测量方式下基本不发生变化;BSF、Sc在同一平衡帽、两种测量方式下得到的结果变化不大,但使用PMMA平衡帽的结果略优于铜制平衡帽。结论:为了满足精确测量和简化方法的要求,建议采用SAD测量方式并使用PMMA平衡帽测量Sc与BSF。

Analysis and Comparison of Two Buildup Caps Made of PMMA and Cu Respectively in Measurement of BSF and Sc for 6MV X ray

Objective： With the comparison of results of back scatter factor （BSF） and collimator scatter factor （Sc） for 6MV X ray, which were measured by used of polymethyimethacrylate （PMMA） and Cu buildup caps, a simple method is intended to be proposed for measuring BSF and So. Material and Method： The PMMA and Cu buildup caps were used to measure BSF and Sc for 6MV X ray in the way of SAD and SSD respectively, and the data is analyzed. Results： In the same measurement condi- tion, absorbed dose of Cu buildup cap is larger obviously; In different buildup cap materials and different measurement methods, the value and the change tendency of Se basically unchanged; In the different measurement methods but with the same buildup cap material, BSF and Sc changed little, however, the use of PMMA build cap is slightly better than Cu. Conclusion： In order to measure accurately and simply, a method of using PMMA buildup cap to measure BSF and Sc at the distance of SAD is rec- ommended.