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Interplay – Active scanning
•
Interference effects of target motion and scanned beam can
further cause severe under/over-dosage of the target volume despite
using margins to account for the radiological depth (WEPL based
geometry).
•
The dose uniformity is very dependent on the motion amplitude
and the relative direction of beam motion and target motion.
•
Multiple irradiations of the volume decrease the sensitivity to
these interference effects
→
rescanning (statistical averaging of local
over and under-dosage due to interplay effect)
•
SFUD planning, multiple fields and fractionation are a type of re-
scanning.