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Influence of margin on volume
• GTV, 2 cm diameter, volume 4.2 cm
3
•
Add 1 cm to
• CTV, 4 cm diameter, volume 33.5 cm
3
•
Add 1 cm to
•
PTV, 6 cm diameter, volume 113 cm
3
GTV
CTV
PTV
Verellen D, Ridder MD, Linthout N, Tournel K, Soete G, Storme G: Innovations in image-guided radiotherapy. Nat
Rev Cancer 2007, 7(12):949-960.
• Third-power relationship between radius of
a sphere and volume (4/3π
r
3
)
• Small reduction in margin (5mm) yields a
50% reduction in volume
• The volume of the outer layer equals the
volume of the core of the orange