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Brachytherapy Q is source/position dependent…
photon fluence vs distance per starting particle emitted from a
point 125Ι (top) and 192Ir (bottom) source centered in a 15cm
radius water phantom, multiplied by distance squared
may be considerable
(especially for low E)
BUT
•
They are source dependent
(source materials)
•
and position dependent (source
spectra vary with distance,
angle)
especially
for high Z detectors
Figure from: Papagiannis, Pantelis, Karaiskos, Br J Radiol (2014) 87: 20140163
rel
bq
k rel
f
,