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Margins for random errors

Dose level

PTV margin

PTV margin*

(

ψ

= 3.2 mm)

80%

0.84

√ (σ

²

+ ψ

²

) − 0.84 ψ

0.4

σ

85%

1.03

√ (σ

²

+ ψ

²

) − 1.03 ψ

0.5

σ

90%

1.28

√ (σ

²

+ ψ

²

) − 1.28 ψ

0.6

σ

95%

1.64

√ (σ

²

+ ψ

²

) − 1.64 ψ

0.7

σ

*linear approximation

σ

= SD of random errors,

ψ

=

σ

of Gaussian penumbra