Physics Bucharest 2017

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.