Total margin
=
Σ
+ = 2.5Σ + 1.64
Σ = Σ
2
+ Σ
+
−
+ = 2.5Σ + 0.7 ′
′ =
′ cm
0.7 ′
1.64 ′
+ 0.32
− 0.32
A 5 mm distance between the
95% and 50% isodose surface
corresponds to
s
p
=3.2 mm