5.5 - Errors In Radiotherapy Setup

What is the difference between systematic and random setup error?

Systematic setup errors occur when a patient is set up using incorrect positioning information. This could be because information has been entered incorrectly into the record/verify system, due to inaccurate determination of the isocentre in the bunker, or incorrect positioning of the lasers within the bunker.

Random setup errors occur when the patient's position is incorrect due to daily fluctuations - perhaps their bladder is a bit fuller than the day before, or the temperature in the bunker is slightly different so the immobilisation devices have a minor change in their size. Random errors fluctuate around a certain point.