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Margins and the “van Herk recipe”
•
A short refreshment on the “philosophy”
Ø
“
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
Ø
SHIFT
the blurred dose with the
preparation
error (
systematic
error
):
Σ
Ø
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
Ø
… this gives you the required margin.
SBRT 2017 - D. Verellen