188 / 1542
Assumptions/simplifications in derivation
of M
PTV,i
= 2.5Σ
i
+0.7σ
i
:
- large number of fractions
- spherical tumor
- ideal conformality:
- 95% isodose is a spherical surface coinciding with PTV surface
(ICRU-50: 100% of PTV should get dose ≥ 95%)
- only translational set-up errors:
- no tumor rotations
- no deformations
(derived margin often has to be considered as lower limit)