856 / 1224
Brachy dosimetry is challenging …
for an Ir-192 HDR source
K
S
zyD
) , (
.
Dose rate varies from ~20 Gy/s @
(0.5cm,90
0
) from an Ir-192 HDR source
to ~2 μGy/s @ (5cm,90
0
) from an I-125
LDR source
Sensitivity high for low uncertainty, dose
range high, (preferably) with k
l
=k
dr
=1
Spatial dose gradient is high (i.e.
~25%/mm in the radial direction @
(0.5cm,90
0
) from an Ir-192 HDR source)
Volume must be small, positional
accuracy is very important
(1% rel. uncert. in D(1cm,90
0
) requires
0.05mm uncertainty in r, assuming 1/r
2
dose dependence since:
)
If solid phantoms are used to increase
positional accuracy a correction is
required from D
w,phant
to D
w,w
at each
meas. position
r
D
r
D
2
=
Figure from: Taylor, Yegin, Rogers, Med. Phys. 34(2) 445 (2007)