Edwards Stephen, Schick Daniel
*Biomedical Technology Services, The Prince Charles Hospital, Rode Road, Chermside, Queensland, Australia 4032; †Biomedical Technology Services, Princess Alexandra Hospital, Ipswich Road, Woolloongabba, Queensland, Australia 4101.
Health Phys. 2016 Apr;110(4):328-41. doi: 10.1097/HP.0000000000000474.
Radiation protection for clinical staff and members of the public is of paramount importance, particularly in occupied areas adjacent to computed tomography scanner suites. Increased patient workloads and the adoption of multi-slice scanning systems may make unshielded secondary scatter from ceiling surfaces a significant contributor to dose. The present paper expands upon an existing analytical model for calculating ceiling scatter accounting for variable room geometries and provides calibration data for a range of clinical beam qualities. The practical effect of gantry, false ceiling, and wall attenuation in limiting ceiling scatter is also explored and incorporated into the model. Monte Carlo simulations were used to calibrate the model for scatter from both concrete and lead surfaces. Gantry attenuation experimental data showed an effective blocking of scatter directed toward the ceiling at angles up to 20-30° from the vertical for the scanners examined. The contribution of ceiling scatter from computed tomography operation to the effective dose of individuals in areas surrounding the scanner suite could be significant and therefore should be considered in shielding design according to the proposed analytical model.
临床工作人员和公众的辐射防护至关重要，尤其是在紧邻计算机断层扫描（CT）扫描仪室的人员占用区域。患者工作量的增加以及多层扫描系统的采用，可能使来自天花板表面的未屏蔽二次散射成为剂量的重要贡献源。本文扩展了一个现有的分析模型，该模型用于计算考虑可变房间几何形状的天花板散射，并提供了一系列临床射束质量的校准数据。还探讨了机架、假天花板和墙壁衰减对限制天花板散射的实际影响，并将其纳入模型。使用蒙特卡罗模拟对来自混凝土和铅表面的散射模型进行校准。机架衰减实验数据表明，对于所检查的扫描仪，在与垂直方向夹角高达20 - 30°时，可有效阻挡射向天花板的散射。根据所提出的分析模型，CT操作产生的天花板散射对扫描仪室周围区域人员有效剂量的贡献可能很大，因此在屏蔽设计中应予以考虑。
