低剂量螺旋CT扫描对肺癌模拟定位应用价值

Practical value of low-dose CT scanning in simulated location of lung cancer

目的探讨低剂量螺旋cT扫描在肺癌模拟定位的可行性。方法选择确诊为肺癌患者62例。在电压120kV、层厚5mm、螺距1：1、扫描时间1s条件下按20、100mA依次扫描2次，按优、良、差评价图像质量。利用治疗计划系统测定肿瘤靶区，记录单次扫描加权剂量指数、z轴扫描范围、剂量长度乘积用于估算患者受照剂量。对cT图像质量和肿瘤大小、组间剂量差异分别行Fisher’s精确概率法和配对t检验。结果低剂量与高剂量扫描的图像质量相似（优、良、差分别为46、13、3例与50、11、1例，P=0．541），同一肿瘤的靶区大小也相似（36．78、40．35cm3，t=2．57，P=0．189），低剂量扫描剂量远小于高剂量的（133．05、941．25mGy，t=一41．24，P=0．000）。结论采用20mA管电流螺旋CT模拟定位扫描能基本保证靶区勾画和扫描图像质量，明显减少照射剂量对患者造成的可能伤害。

Objective This paper studies on feasibility of low dose CT scanning in lung cancer patients simulated localisation. Methods 62 patients cases of lung cancer are selected. Scan parameter： scan twice by 20/100 mA, the other parameter remain unchanged as voltage of 120 kV, thickness of 5 mm, pitch of 1：1 and scan time of 1 s. After scan, picture quality was evaluated according to excellent, good, bad under different condition. Volume of target was determined by treatment planning system. Data such as dose index value of single helical scan, z-axis scan range, dose length product value and etc. are recorded in order to evaluate radiation dose of patients. Picture quality and the difference of radiation dose were statistically analyzed using Fisher＇s and pair t-test. Results Picture quality of low dose scanning was a little bit lower than that of normal dose, however, picture quality difference of difference dose scanning was statistically meaningless （ number of patients according to excellent, good, bad were 46,13, 3 and 50,11,1, P=0. 541 ）. There is no obvious difference of target volume under different dose scanning in the same （36. 78 cm3 ,40. 35 cm3, t = 2. 57, P = 0. 189）. Radiation dose of low dose scanning group is far less than that of high dose scanning group and the difference is obvious （ 133.05 mGy,941.25 mGy,t = -41.24,P = 0. 000）. Conclusions Low dose scanning of 20 mA current during CT simulated localisation tremendously reduces harm that may happen to patients during CT scan, while tumor target delineation and scanned picture quality is guaranteed.