目的 研究西门子 Sensation Open CT模拟机的Med-Tec CT碳纤维平板床和ORFIT AIO碳纤维放疗定位底板对水的CT值的影响.方法对3种水模体摆放情形进行研究:情形A 水模体悬空放置;情形B 水模体放置在CT平板床上;情形C 在水模体和CT平板床之间放置一个ORFIT AIO放疗定位底板.应用6种放疗扫描协议,在上述3种情形下对水模体进行扫描,获取CT图像.在每张CT图像上勾画出5个圆形区域,获取这些区域中水的平均CT值(记为Yw).结果情形B中Yw值均低于情形A;情形C中Yw值高于情形B;情形C中Yw值均低于情形A.结论把CT碳纤维平板床放在水模体下,会降低CT图像中水的CT值;在水模体和CT平板床之间加入AIO定位底板,会把上述降低作用削弱.在对CT模拟机进行质量控制检验时需注意水模体的正确摆放位置.%Objective To investigate influence of the Med-Tec CT-carbon fibre couch of Siemens Sensation Open CT simulator and the ORFIT AIO carbon fibre immobilization base plate on CT values of water. Methods The following experimental methods are utilized to carry out the work. 3 cases about the water phantom position are used to experiment: A the water phantom is suspended in the air; B the water phantom is placed on the CT-carbon fibre couch; C an ORIFIT AIO base plate is positioned between the water phantom and CT-carbon fibre couch closely. 6 radiotherapeutic scanning protocols have been used for the above 3 cases to obtain CT images. In each image, 5 circular areas are drawn to get the mean CT value of water (Yw) for each area. Results All values of Yw in case B are lower than corresponding values in case A. On the whole, values of Yw in case C are higher than corresponding values in case B. All values of Yw in case C are lower than corresponding values in case A. Conclusion It would decrease CT values of water in CT images, by placing the CT-carbon fibre couch under the water phantom. It would weaken the above decrease influence, by placing the AIO immobilization base plate between the water phantom and the CT-carbon fibre couch. Therefore, it should be paid attention to the correct position of water phantom, when carrying out quality control procedures for the CT simulator.
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