Martin C J
Department of Bio-Medical Physics and Bio-Engineering, Aberdeen Royal Hospitals-NHS Trust, Foresterhill, UK.
Phys Med Biol. 1995 May;40(5):823-34. doi: 10.1088/0031-9155/40/5/008.
Measurements of patient entrance surface dose rate provide valuable data for interpreting results from dose-area product studies on fluoroscopic x-ray equipment. Methods for measurement of entrance surface dose rate with backscatter and incident dose rate without backscatter have been investigated. Entrance surface dose rate is measured with an ionization chamber in contact with a tissue-equivalent phantom. Backscattered radiation contributes 27-45% to the measurement and is affected by field size and chamber position. Incident dose rate measured using a copper phantom provides an alternative approach. Consistent relationships between thicknesses of Perspex and copper giving similar incident dose rates under automatic gain control have been established for different tube potentials with and without a grid. This allows measurements of incident dose rate made using copper to be linked to corresponding thicknesses of tissue-equivalent material. Since only a few millimetres of copper are required, contributions from backscatter can be minimized and transport of phantoms is simplified. Incident dose can be related to dose-area product and entrance surface dose derived using backscatter factors. Such measurements play a valuable role in interpreting patient dose data and recommending options to reduce patient dose.
患者体表剂量率的测量为解释荧光透视X射线设备剂量面积乘积研究的结果提供了有价值的数据。已经研究了测量带有反向散射的体表剂量率和不带有反向散射的入射剂量率的方法。体表剂量率是用与组织等效体模接触的电离室进行测量的。反向散射辐射对测量的贡献为27%至45%，并受射野大小和电离室位置的影响。使用铜体模测量的入射剂量率提供了一种替代方法。对于有和没有滤线栅的不同管电压，已经建立了在自动增益控制下产生相似入射剂量率的有机玻璃厚度与铜厚度之间的一致关系。这使得使用铜进行的入射剂量率测量能够与组织等效材料的相应厚度相关联。由于只需要几毫米厚的铜，反向散射的贡献可以最小化，体模的运输也得以简化。入射剂量可以与剂量面积乘积以及使用反向散射因子得出的体表剂量相关。此类测量在解释患者剂量数据以及推荐降低患者剂量的方案方面发挥着重要作用。
