MRI用于立体定向放射治疗定位的精确性分析

目的：研究MRI用于立体定向放射治疗（SRT）定位时误差的大小，明确MRI能否单独用于SRT定位。方法：模拟对病人的扫描方法，对特制体模进行固定和MRI扫描。在治疗计划系统上，测量x、y、z3个方向靶点距离，并将结果与实际距离做比较，差别的绝对值即为该定位系统的误差。结果：相邻点x方向，误差0.2～1.4mm，平均0．9mm；y方向误差0.5～1.5mm，平均0．9mm。相对点x方向，误差0.3～1．7mm，平均0.9mm；y方向，误差0.4～1．8mm，平均0．9mm。各标记层面之间误差无显著性差别（P〉0．05）。z方向误差0．3～1.9mm，平均1．0mm。结论：本研究采用的立体定向定位系统和MRI扫描方法，用MRI进行影像采集制定SRT计划，对多数颅内和头颈部肿瘤的定位精度符合临床要求，但在将MRI进行SRT定位扫描时，必须作全面的检查和验证。

Accuracy of magnetic resonance imaging in the localization of stereotactic radiotherapy

Objective: To measure the errors of magnetic resonance imaging(MRI) in the localization of stereotactic radiotherapy(SRT),and to confirm whether MRI can be used in the localization alone.Methods: A specially made phantom was used to acquire MRI images.In the treatment planning system,the distances between targets in x,y,and z directions were measured and compared with true values.The absolute values of the differences between the measured and true values were considered as the errors of the localization system.Results: The errors of adjacent points were in the range of 0.2 to 1.4 mm and 0.3 to 1.5 mm in x and y directions,respectively,and the average was 0.9 mm in both x and y directions.The errors of opposite points were in the range of 0.3 to 1.7 mm and 0.4 to 1.8 mm in x and y directions,respectively,and the average was 0.9 mm in both x and y directions.There was no significant difference among 6 marked planes in both x and y directions(P > 0.05).Errors in z direction were in the range of 0.3 to 1.9 mm,and the average was 1.0 mm.Conclusion: MRI can be used alone in the localization of most brain tumors and head and neck tumors,but it is necessary to perform a comprehensive check when MRI is used in SRT localization.