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Margins and the “van Herk recipe”
•
A short refreshment on the “philosophy”
“
Blur
” the planned dose distribution using
all execution
(random) errors
(i.e. set-up, inter/intra fraction motion,
penumbra, …) to estimate the cumulative dose distribution:
σ
Shift
the blurred dose with
the
preparation
error (
systemetic
error
):
Σ
Use a probability distribution of preparation errors to compute the
fraction of patients that receive a certain dose to the CTV:
For a given dose level:
Find the region of space where the cumulative dose exceeds the given
dose level.
Compute the
probability
that the CTV is in that region
… this gives you the required margin.
The PTV 2017 - D. Verellen