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2D vs 3D setup
Phantom test: identical
Detected error in CBCT larger in all
directions
CBCT measurements better reproducable
Fuller et al. 2009
2D vs 3D setup correction
Planar imaging underestimates the setup
error, especially if you do it manually
Deformation might contribute to this (Li et al)
• Purple: reference CT
scan
• Green: daily
localization Cone
Beam CT scan
• Need for choices in
alignment!
How flexible is the neck ?
• PTV conflicts with OAR
• You cannot align all
at the same time:
Compromise!
How flexible is the neck ?
31 patients
8 CBCT scans per patient:
249 scans evaluated
9 ROIs per patient
Retrospectively:
Larynx assumed as PTV
Vertebrae assumed as OAR
How flexible is the neck ?
How flexible is the neck ?
Count occurrence of ROI
within certain margin
ROI:
• PTV(larynx)
• OAR (C3-C5)
Margin 0..10 mm (1 mm)