Electron return effect and its impact on MRRT

Experts from Tübingen University Hospital in Germany explain what the electron return effect (ERE) is and they discuss whether this has an impact on treatment delivery when using an MR-Linac

What is ERE?

• ERE refers to the effect of electrons returning to normal after exiting the patient’s surface.
• In a single field or standard orientation, this can cause a high dose near the skin.

How is it accounted for?

• Constraint optimization, which considers beam angles, is used to address ERE.
• Clinical plans are designed to handle this effect effectively.

What is the clinical impact of ERE?

• The goal is to minimize high-dose hot spots caused by ERE. While the effect is generally small, it’s important to optimize it.
• There has been no significant indication of increased toxicity due to ERE.

What happens if the anatomy changes?

• Changes like air pockets may appear during adaptation.
• Test scenarios show no significant impact on the dose distribution with a 1-fraction adaptation.

What has been your clinical experience so far?

• ERE is more relevant when treating rectal tumors due to the presence of air in the rectum.  
• However, dramatic hot spots have not been observed in adaptive plans to date.

Find out more:
Elekta Unity | MR-Linac - MR/RT | Radiotherapy | Elekta