IMRT

CTV-PTV margin calculation

Prediction error tolerance level of 3 mm

σ = 1.5 mm (dose blurring) Σ= 1.5 mm (shift)

3 mm

3 mm

1.5 mm

R=3 mm

rebuild CM

Mechanical tracking errors

Penumbra: σ p =4.05mm β=0.73 (for 80% isodose)

marker-TV surrogate uncertainty

Gimbals systematic error

+

Correlation model Fit errors ( σ = 1 mm)

σ = 0.5 mm

Σ=CT-slice/2=1 mm

Σ= 0.4 mm

M=2.5*√(( 1mm ) 2 +( 1.5mm ) 2 +( 0.4mm ) 2 )+0.73*√(( 1.5mm ) 2 +( 0.5mm ) 2 +( 1mm ) 2 +(4.05mm) 2 )-0.73*4.05mm =4.9 mm => 5 mm

Based on Van Herk et al. 2000