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TLD: absorbed dose energy dependence
•
TLD dose changes more than water at Q<<Q
0
due to higher Z than water, so f
rel
<1
A i
TLD i
l
it (di
i
)0(
)0(
) (
) (
)0 , (
Q TLDDQwD
Q TLDDQwD
QQ rel f
•
ssum ng
s a arge cav y mens ons
large compared to max. e
-
range & small
compared to photon m.f.p.):
for LDR sources relative to Co 60
7.0
)0(
)
(
) (
)
(
)0 , (
Q w
TLD en
Q w
TLD en
QQ rel f
- .
This is only an approximation.
•
MC is used to account for:
•
photon spectra @ each point in Q, Q
0
•
TLD attenuation,
•
v. averaging
•
cavity corrections, … etc.
See: Rodriguez and Rogers, Med. Phys. 41(11) p.
114301 (2014) for an excellent review…!
Figure from: Rogers & Cygler (Eds), Clinical dosimetry measurements in radiotherapy
(2009 AAPM Summer School), Monograph No. 34, Medical Physics Publishing 2011