Table 6 Principal component analysis of the placement variations of the transducer arrays: coordinates of the principal components. X, y, and z are the coordinates of a central electrode of the respective array in the CT-coordinate system relative to the electrode mean position over all fractions. Unit of length is cm

p1 = −0.077^.x + 0.919^.y + 0.386^.z

65.7%

p2 = 0.993^.x + 0.038^.y + 0.110^.z

28.8%

p3 = − 0.087^.x - 0.392^.y + 0.916^.z

5.5%

p1 = − 0.058^.x - 0.459^.y + 0.887^.z

72.8%

p2 = 0.997^.x - 0.063^.y - 0.033^.z

24.1%

p3 = 0.041^.x + 0.886^.y + 0.461^.z

3.1%

p1 = 0.231^.x + 0.891^.y - 0.390^.z

56.8%

p2 = − 0.305^.x + 0.447^.y + 0.841^.z

38.4%

p3 = 0.924^.x - 0.076^.y + 0.375^.z

4.8%

p1 = 0.017^.x + 0.993^.y - 0.119^.z

70.0%

p2 = 0.345^.x + 0.1096^.y + 0.933^.z

26.3%

p3 = 0.939^.x - 0.057^.y - 0.340^.z

3.7%