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Margins for random errors
Dose level
PTV margin
PTV margin*
(
y
= 3.2 mm)
80%
0.84
s
²
+ y
²
) - 0.84 y
0.4
s
85%
1.03
s
²
+ y
²
) - 1.03 y
0.5
s
90%
1.28
s
²
+ y
²
) - 1.28 y
0.6
s
95%
1.64
s
²
+ y
²
) - 1.64 y
0.7
s
*linear approximation
s
= SD of random errors,
y
=
s
of Gaussian penumbra