Gao Liugang, Sun Hongfei, Ni Xinye, Fang Mingming, Lin Tao
Radiotherapy Department, Second People's Hospital of Changzhou, Nanjing Medical University, Changzhou 213003, P.R. China.
Radiotherapy Department, Changzhou Cancer Hospital of Soochow University, Changzhou 213001, P.R. China.
Oncol Lett. 2018 Feb;15(2):2373-2379. doi: 10.3892/ol.2017.7586. Epub 2017 Dec 11.
Dose distribution was calculated and analyzed on the basis of 16-bit computed tomography (CT) images in order to investigate the effect of scanning conditions on CT for metal implants. Stainless steel and titanium rods were inserted into a phantom, and CT images were obtained by scanning the phantom under various scanning conditions: i) Fixed tube current of 230 mA and tube voltages of 100, 120, and 140 kV; and ii) fixed tube voltage of 120 kV and tube currents of 180, 230, and 280 mA. The CT value of the metal rod was examined and corrected. In a Varian treatment planning system, a treatment plan was designed on the basis of the CT images obtained under the set scanning conditions. The dose distributions in the phantom were then calculated and compared. The CT value of the metal area slightly changed upon tube current alteration. The dose distribution in the phantom was also similar. The maximum CT values of the stainless steel rod were 14,568, 14,127 and 13,295 HU when the tube voltages were modified to 100, 120, and 140 kV, respectively. The corresponding CT values of the titanium rod were 9,420, 8,140 and 7,310 HU. The dose distribution of the radiotherapy plan changed significantly as the tube voltage varied. Compared with the reference dose, the respective maximum dose differences of the stainless steel and titanium rods in the phantom were 5.70, and 6.62% when the tube voltage varied. The changes in tube currents resulted in a maximum dose error of <1% for stainless steel and titanium. In CT imaging, changes in tube voltages can significantly alter the CT values of metal implants. Thus, this can lead to large errors in radiotherapy dose distributions.
为了研究扫描条件对金属植入物CT成像的影响，基于16位计算机断层扫描（CT）图像计算并分析了剂量分布。将不锈钢和钛棒插入模体中，并在各种扫描条件下对模体进行扫描以获取CT图像：i）管电流固定为230 mA，管电压分别为100、120和140 kV；ii）管电压固定为120 kV，管电流分别为180、230和280 mA。检测并校正了金属棒的CT值。在Varian治疗计划系统中，根据在设定扫描条件下获得的CT图像设计治疗计划。然后计算并比较模体中的剂量分布。管电流改变时，金属区域的CT值略有变化。模体中的剂量分布也相似。当管电压分别调整为100、120和140 kV时，不锈钢棒的最大CT值分别为14568、14127和13295 HU。钛棒的相应CT值分别为9420、8140和7310 HU。放疗计划的剂量分布随管电压变化而显著改变。与参考剂量相比，当管电压变化时，模体中不锈钢棒和钛棒各自的最大剂量差异分别为5.70%和6.62%。管电流的变化导致不锈钢和钛的最大剂量误差<1%。在CT成像中，管电压的变化会显著改变金属植入物的CT值。因此，这可能导致放疗剂量分布出现较大误差。
