Objective:To explore the feasibility of low-doses scan for lung cancer simulation positioning with spiral CT. Methods: A total of 160 lung cancer patients were selected and divided into control and test group randomly, 80 patients in each group. Then, scan simulation position was carried out with spiral CT to each cases. The major parameters of CT machine were same in each group (voltage: 120KV, scanning layer thick: 5mm, step-length: 1.0 cm, scan-time: 1 second), but tube-current value was different: 120 mA in control group, and 15, 30, 60, 120 mA in test group (four times order scan). To evaluate scan-image obtained at different tube-current value, evaluated Image into 4 levels (very good, good, general and poor). Target size of tumor, transfer the CT image to TPS positioning system and draw the outline of tumor were determined. To estimate CT radiation harm to patients, calculate radiation dose according to CTDI of each single helical scanning, scanning scope of Z axis, CDLP and other data. Finally, to determine if there is statistical difference in image quality, target image size and radiation dose under different tube-current value, all results were analyzed using Fisher precision probability analysis and other methods in SPSS 13.0 software-set. Results: (1) The image quality with 120 mA is a bit better than that with 60, 30 and 15 mA, but there is no statistical difference between the two group (P = 0. 572). (2) Target sizes of same tumor mass under different tube-current value no significant difference (P = 0. 12). (3) The radiation-dose of test group is much lower than that of control group, the difference is very significant (P＜0. 001), even if there are accumulate effect in test group. Conclusions: Using of low-dose scanning in lung tumor CT simulation positioning will not cause evident information lose for target area size and scanning image, and can reduce the radiation harm of patients.%目的:探讨低剂量CT扫描在肺癌模拟定位中的可行性.方法:选择确诊为肺癌的患者160例,随机分成对照组和试验组,每组各80例.扫描时,对照组管电流为120 mA,试验组依次按照15、30、60、120 mA依次扫描4次.其他参数2组一致,均为电压120 KV,层厚5 mm,螺距1.0 cm,扫描时间1 s.扫描后,按照"很好、好、一般、差"将不同条件下得到的图像质量评价4级;利用TPS定位系统测定肿瘤靶区大小;分别记录单次螺旋扫描的剂量指数(CTDI) 值、Z轴扫描范围、剂量长度(CDLP)值等数据,用于估算患者受照的辐射剂量.用Fisher精度概率分析等方法对图像质量、图像大小和辐射剂量差异进行统计学分析.结果:(1)低剂量扫描的图像质量略低于常规剂量,但各剂量组的图像质量差异无统计学意义(P=0.572);(2)同一肿瘤在不同剂量下得到的靶区轮廓大小无显著差异(P=0.12);(3)即使在辐射累积的条件下,试验组的辐射剂量也远小于对照组,差异极显著(P<0.001).结论:在CT模拟定位时采用15 mA管电流的低剂量扫描可以在基本保证肿瘤靶区勾画和扫描图像质量的前提下,明显减少CT扫描辐射对患者造成的可能伤害.
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