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For low energy sources, simulations must also account for the WAFAC - 7.6
o
half
angle
.
Figure from : J. F. Williamson, Med. Phys. 27 (4) 643 2000
Geometry for actual measurement of
S
K
•
Due to polar angle
averaging, S
K
increases
for
sources with
radioactivity distributed
over cyl. ends, leading
to Λ
WAFAC
lower than
Λ
point
results.
•
This effect depends on
the ratio of marker
diameter to marker
length.
•
Differences between
Λ
WAFAC
and Λ
point
range
from non-detectable to
3.5%.