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simplified depth dose formalism
DD(d)
%
=D
max •
(f+d
m
/f+d)
2
•
e
-(
m
•
d)
•
K
s
f
distance from source to surface
d
m
or depth to
D
max
d
is depth in tissue
K
s
is the scatter
attenuationscatte
r
distanc
e
Dose build-up region
D
max
Surface
Dose D
S
Exit
Dose
D
ex
Shape of a MV photon beam PDD
A
B
C
DD(d)
%
=D
max •
(f+d
m
/f+d)
2
•
e
-(
m
•
d)
•
K
s