CT扫描对靶点位置精确度影响分析

目的 研究CT扫描条件变化对利用z形定位框架定位的WIMRT治疗系统计算坐标的影响.方法 分别在定位框架横向倾斜、CT机架倾斜、定位框架轴向与CT进床方向不重合条件下全头模范围扫描,图像传输到计划系统,计算头模内不同位置的3个靶点的坐标,与标准条件下扫描计算的坐标进行比较.结果 根据定位框架横向倾斜时获得的定位图像计算的靶点坐标高度、宽度值有偏差,倾斜角越大,偏差越大.且靶点宽度坐标绝对值大小会影响计算高度坐标偏差,宽度值越大,高度坐标偏差有变大的趋势;同样,靶点高度绝对值与宽度坐标计算值偏差也有以上关系.CT机架不归零、定位框架轴向与CT进床方向倾斜主要影响靶点长度坐标计算值.结论 定位时必须派有资质的物理师严格按照定位的标准条件扫描.

Impact of CT scanning condition on the precision and accuracy of target position

Objective To study the effect of CT scanning condition on the target position coordinate with WIMRT radiotherapy planning system using the" Z" form localizing frame. Methods The whole Head Phantom containing three metal targets was scanned under the following conditions: localizing frame transver-sally tilting, CT gantry tilting and localizing frame axially tilting. Then the three target coordinates were com-puted respectively and compared with those under the standard condition. Results The height and width of coordinate under the localizing frame transversally tilting condition deviated from those under the standard scanning condition,which was in an angle dependent manner. On the other hand ,a tendency was shown that the greater the absolute height value of the targets coordinate, the greater the width value deviation. And so was the relation between the absolute width value of the coordinate and height value deviation. If CT gantry angle was not zero degree or localizing frame axis is not in the same line with the CT bed moving direction, the calculated longititude value of the targets coordinate was mainly affected. Conclusions CT scanning must be performed strictly under the standard localizing scanning condition by a proficient physicist.