IMRT 2018

Interplay effect

• Total dose distribution relies on different areas of the target being selectively exposed at different times • Intrafraction motion would lead to the dose accumulating in a different distribution than planned In reality, the interplay effect is rarely a problem:

• Over many fractions the dose averages out • SABR: few fractions but longer delivery times (e.g. more breathing cycles) • Very heavily modulated plans, single-arc VMAT • Avoid by limiting modulation

06/06/2018