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Table 2 Systematic change in distance between the subregions due to rotation and shape changes of the bony landmarks

From: Estimation of adequate setup margins and threshold for position errors requiring immediate attention in head and neck cancer radiotherapy based on 2D image guidance

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)

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