2017_IGRT course book

How to choose the PTV margin

• Express required CTV dose for a specified fraction of patients. For example: 90% of the patients must get a minimum CTV dose of 95% or more

• Add first margin so that 90% of the preparation (systematic) errors are covered

• Add margin for penumbra and execution (random) variation so that CTV + first margin lies within the 95% isodose