Brix G, Lechel U, Veit R, Truckenbrodt R, Stamm G, Coppenrath E M, Griebel J, Nagel H-D
Department of Radiation Protection and Health, Division of Medical Radiation Hygiene and Dosimetry, Federal Office for Radiation Protection, 85764 Neuherberg, Germany.
Eur Radiol. 2004 Jul;14(7):1275-84. doi: 10.1007/s00330-004-2267-7. Epub 2004 Mar 19.
Dose assessment in computed tomography (CT) is challenging due to the vast variety of CT scanners and imaging protocols in use. In the present study, the accurateness of a theoretical formalism implemented in the PC program CT-EXPO for dose calculation was evaluated by means of phantom measurements. Phantom measurements were performed with four 1-slice, four 4-slice and two 16-slice spiral CT scanners. Firstly, scanner-specific nCTDIw values were measured and compared with the corresponding standard values used for dose calculation. Secondly, effective doses were determined for three CT scans (head, chest and pelvis) performed at each of the ten installations from readings of thermoluminescent dosimeters distributed inside an anthropomorphic Alderson phantom and compared with the corresponding dose values computed with CT-EXPO. Differences between standard and individually measured nCTDIw values were less than 16%. Statistical analysis yielded a highly significant correlation (P < 0.001) between calculated and measured effective doses. The systematic and random uncertainty of the dose values calculated using standard nCTDIw values was about -9 and +/- 11%, respectively. The phantom measurements and model calculations were carried out for a variety of CT scanners and representative scan protocols validate the reliability of the dosimetric formalism considered-at least for patients with a standard body size and a tube voltage of 120 kV selected for the majority of CT scans performed in our study.
由于使用的CT扫描仪和成像协议种类繁多，计算机断层扫描（CT）中的剂量评估具有挑战性。在本研究中，通过体模测量评估了PC程序CT-EXPO中用于剂量计算的理论形式的准确性。使用四台1层、四台4层和两台16层螺旋CT扫描仪进行体模测量。首先，测量特定扫描仪的nCTDIw值，并与用于剂量计算的相应标准值进行比较。其次，根据分布在拟人化Alderson体模内的热释光剂量计的读数，确定在十个装置中的每一个装置上进行的三次CT扫描（头部、胸部和骨盆）的有效剂量，并与用CT-EXPO计算的相应剂量值进行比较。标准nCTDIw值与单独测量值之间的差异小于16%。统计分析得出计算有效剂量与测量有效剂量之间存在高度显著的相关性（P < 0.001）。使用标准nCTDIw值计算的剂量值的系统不确定性和随机不确定性分别约为-9%和±11%。针对各种CT扫描仪和代表性扫描协议进行了体模测量和模型计算，验证了所考虑的剂量学形式的可靠性——至少对于我们研究中大多数CT扫描所选择的标准体型患者和120 kV管电压而言是如此。
