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pencil kernel parameterization:
Math curiosity, goes to infinity when r->0.
( )
e
e
,
z
z
a r
b r
z
z
A
B
p
r z
r
r
−
−
=
+
Dose on the main axis for a circular field of fluence
:
( )
( )
( )
2
circular
0 0
field
, d
,
d
R
R
p
p
D z
r z A
r z r r
=
=
=
what happens when field size R goes to zero?
2
0 0
e
e
d
z
z
R
a r
b r
z
z
A
B
r r
r
r
−
−
=
+
=
(
)
(
)
1 e
1 e
2
z
z
a R
b R
z
z
z
z
A
B
a
b
−
−
−
−
=
+
Ahnesjö et al (1992)
Med Phys
19, 263-273