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Unexpected shifts
•
Patient CBCT after first
fraction 8 mm shift
•
Suspected to slide down
gradually
•
Next fractions CBCT after
first arc: shift of 3 mm
same direction. Corrected
•
After second arc: again
shift of 3 mm same
direction
•
Decision to continue this
way
•
Next fractions shifts ≤ 3
mm.