Table 2.

Systematic change in distance between the subregions due to rotation and shape changes of the bony landmarks

Subregions	Practical importance	AP/ vertical	CC/ longitudinal	LAT/ lateral
C1-2 and C5-7	Rotation of the vertebrae	3.1 mm	1.2 mm	2.3 mm
		ρ = −0.34 (−0.21)	ρ = 0.55 (0.82)	ρ = −0.14 (−0.06)
C5-7 and occiput bone	Rotation of patient	3.4 mm	1.5 mm	-
		ρ = −0.34 (−0.26)	ρ = 0.34 (0.63)
C1-2 and occiput bone	Orientation of vertebrae and skull base	1.9 mm	1.3 mm	-
		ρ = 0.69 (0.60)	ρ = 0.55 (0.66)
Mandible and occiput bone	Nod movement of the head	2.6 mm	4.0 mm	-
		ρ = 0.42 (0.37)	ρ = −0.27 (−0.27)
Mandible and C1-2	Independent movement of mandible	2.2 mm	2.9 mm	1.5 mm
		ρ = 0.61 (0.30)	ρ = 0.12 (−0.22)	ρ = 0.62 (0.57)

Also correlation coefficients (ρ) for the position errors are given for MID_PTV and (MIN_MAX) image matches.