496 / 1359
Ahnesjö et al (1992)
Med Phys
19, 263-73
In the same way, the dose to the central
axis from a square field, with side
s
,
can be
calculated by employing the equivalent
circle with
R
=0.561
·
s
.
calculation techniques:
A particular simple case is dose at the main axis for circular fields of radius
R
with
homogeneous energy fluence:
( )
( )
(
)
(
)
2
0 0
e
e
d
1 e
1 e
2
z
z
z
z
R
a r
b r
z
z
a R
b R
z
z
z
z
A B
D z
r r
r
A
B
D
z
a
b
−
−
−
−
+
=
−
−
=
+
Bjärngard and Siddon (1982).
Med Phys
9, 258-60