MRI定位伽马刀治疗精度的检测与修正

目的 探讨MRI定位伽马刀治疗精度的检测与修正方法。方法 利用25点矩阵水箱对伽马刀治疗精度进行多点检测,将MRI定位坐标与经过CT定位曝光验证、治疗精度偏差<0.5 mm的坐标进行比对,发现MRI定位偏差的大小及图像有无变形,然后按偏差均值±图像几何畸变率给予修正,与标准坐标间无显著差异后再行胶片曝光验证。结果 所测3家医院MRI定位25点矩阵水箱的x、z坐标轴均无明显偏移,在y轴上存在的偏差分别为A院(－1.94±0.45) mm、B院(－2.22±0.29) mm和C院(－1.25±0.21) mm, A院在y轴上尚有1%的几何畸变率。以M表示偏差均值、GD为几何畸变率、Y₀为矩阵中心点坐标,将25点坐标Y分别代入公式Y_修=(Y－M)＋GD (Y₀－Y)修正后,3家医院与标准坐标间均相近,验证片焦斑偏移也在0.5 mm内。结论 利用25点矩阵水箱进行伽马刀治疗精度多点检测和偏差的函数修正,可以明确MRI能否直接用于头部伽马刀定位。

Detection and correction of the accuracy of gamma knife treatment positioned by MRI

Objective To investigate MRI localization the accuracy and correct the deviation for gamma knife treatment. Methds With 25-point-matrix tank, the deviation of MRI localization and its regularities could be identified after the comparison between the coordinates of MRI localization and the ones which have already been verified by CT within the deviation of 0.5 mm. Then the original MRI coordinates will be corrected by the acquired mean deviation and the geometric distortion of images. Afterwards the corrected coordinates will be compared with the standard ones and finally validated by exposure film. ResultsThere are no significant deviations on x-and z-axis after measurement in three hospitals, y-axis, however, bears deviation of (1.94±0.45) mm for hospital A,(－2.22±0.29) mm for hospital B,(－1.25±0.21) mm for hospital C,respectively. Furthermore there also exists geometric distortion of 1% on y-axis in hospital A. The corrected coordinates on y-axis (y_c) will be calculated from the formula:Y_c=(Y－M)+GD (Y₀－Y)(Y:the original coordinates on y-axis, M:the mean of deviation on y-axis, GD:the geometric distortion,Y₀:the coordinate on y-axis of the central point among the 25-point matrix).Once completed, the corrected coordinates of MRI localization is of no significant difference with the standard coordinates verified by CT. Even the deviation of focal spot on validation film is within 0.5 mm. Conclusions The 25-point-matrix tank in the multi-point measurement of the accuracy and the correction of deviation for gamma knife treatment is feasible to determine whether MRI can be utilized in the localization for head gamma knife treatment.