Tsapaki V, Tsalafoutas I A, Chinofoti I, Karageorgi A, Carinou E, Kamenopoulou V, Yakoumakis E N, Koulentianos E D
Medical Physics Unit, General Hospital Konstantopoulio-Agia Olga, Athens, Greece.
Br J Radiol. 2007 Feb;80(950):107-12. doi: 10.1259/bjr/87150291. Epub 2006 Aug 2.
The objective of the study was to derive a mathematical method for calculating the entrance surface dose (ESD) from exposure factors for all tube potentials used in clinical practice and to compare the calculated ESDs (ESD(C)) with those measured (ESD(TLD)) using thermoluminescent dosemeters (TLDs). The exposure parameters of 43 patients who underwent (a) posteroanterior (PA) and lateral (LAT) chest examination (13 patients), (b) supine abdomen (10 patients), (c) erectus abdomen (10 patients), or (d) urinary tract examination (10 patients) were recorded. Patient ESD was directly measured by TLDs and calculated from exposure factors. The differences between ESD(C) and ESD(TLD) were quite small and could be explained by the uncertainties involved in both methods, in all but the PA chest examination where the ESD(C) was about 50% larger than ESD(TLD). However, in PA chest the ESD(TLD) was close to the minimum detectable dose of TLDs, questioning the accuracy of ESD(TLD). Further investigation showed that using the high tube potential technique (130 kV) in the PA chest examination resulted in very short exposure times, in the region of 4 ms. In such short exposure times, the X-ray generator operation presented stability problems that led to loss of output linearity and consequently to false calculation of ESD. The calculation method offers a reliable and cheap alternative to the measurement of ESD by TLD, provided that the exposure times are not as short as in the PA chest examinations recorded in this study, so that the output linearity with tube current-time product (mAs) is maintained.
本研究的目的是推导一种数学方法，用于根据临床实践中使用的所有管电压的曝光因子计算入射表面剂量（ESD），并将计算得到的ESD（ESD(C)）与使用热释光剂量计（TLD）测量的ESD（ESD(TLD)）进行比较。记录了43例接受以下检查的患者的曝光参数：（a）后前位（PA）和侧位（LAT）胸部检查（13例患者）、（b）仰卧位腹部检查（10例患者）、（c）立位腹部检查（10例患者）或（d）泌尿系统检查（10例患者）。通过TLD直接测量患者的ESD，并根据曝光因子进行计算。除了PA胸部检查中ESD(C)比ESD(TLD)大约大50%外，ESD(C)和ESD(TLD)之间的差异非常小，这可以用两种方法所涉及的不确定性来解释。然而，在PA胸部检查中，ESD(TLD)接近TLD的最小可探测剂量，这对ESD(TLD)的准确性提出了质疑。进一步的研究表明，在PA胸部检查中使用高管电压技术（130 kV）会导致曝光时间非常短，在4 ms左右。在如此短的曝光时间内，X射线发生器的运行出现稳定性问题，导致输出线性度丧失，从而导致ESD的错误计算。该计算方法为通过TLD测量ESD提供了一种可靠且廉价的替代方法，前提是曝光时间不像本研究记录的PA胸部检查那样短，以便维持与管电流-时间乘积（mAs）的输出线性度。
