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CTV2PTV margin algorithm design concepts
“
The PTV is the volume, defined in
treatment room coordinates
, to which the
prescribed dose
a
must be delivered
in order to obtain a clinically acceptable and
specified probability that the prescribed dose is actually received by the CTV,
which has an uncertain location
b
”
a
95%
delivered
dose, including delivery (
random
per patient&fraction)
Van Herk
etal
, IJROBP, 2000 pp. 1121–1135:
uncertainties
σ
2
=
σ
2
pos
+
σ
2
mov
… and dose profile “penumbra”
σ
p
b
considering CTV preparation uncertainties
Σ
2
=
Σ
2
CTpos
+
Σ
2
delineation
… (random but
for each patient
systematic
) so that for 90% of the patients the entire CTV is
inside the ITV
(
)
p
2.5
,
M
f
Σ σ σ
= ⋅ +
Margin:
ITV
PTV