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
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