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Intrafractional motion
2 TYPES OF MOTION:
A: Slow drift motion
Mainly posterioly and inferiorly
Can reach large extends over long time
periods
Probably due to pelvic musculature
relaxation or/and
Gradually Moving rectal content
B: Erractic motion
Sudden and transient
Often significant extend
Probably related due to peristaltic motion
C: Combination of A and B
Langen et al, IJROBP,
Volume 71, Issue 4,
15 July 2008