Optically
p
y Stimulated Luminescence
(OSL) dosimetry in radiotherapy
Joanna E.Cygler
yg 1 and Eduardo Yukihara2
The Ottawa Hospital Regional Cancer Centre, Ottawa, Canada
2Department of Physics, Oklahoma State University, Stillwater, Oklahoma
1
The Ottawa
L’Hopital
Hospital
d
d’Ottawa
Ottawa
Regional Cancer Centre
Disclosure
The authors have received research
support from Landauer Inc.
Inc
Outline
•
•
•
•
Principles of OSL dosimetry
OSL readers and stimulation methods
Optically Simulated Luminescence Dosimeters (OSLDs)
Dosimetric characteristics of Al2O3:C OSLDs for
radiotherapy applications
–
–
–
–
–
–
Environmental corrections
Linearity of dose response
Dose-rate dependence
Energy dependence
Directional dependence
Fading
g
• Advantages and disadvantages
• Clinical dosimetry applications
• Summary
OSL dosimetry - Introduction
• OSL known for more than 50 years
• Widely used in luminescence dating
• Highly sensitive Al2O3:C introduced in 90’s
• Developed for personal dosimetry at
Oklahoma State University
OSL dosimetry - Introduction
• Used in the LuxelTM and
InLightTM dosimetry systems
(Landauer Inc.)
• >1.5 million users (25% of world
market)
• Used in space by NASA
• Starting
g to be adopted
p
in
radiotherapy and diagnostic
radiology
LuxelTM (Landauer Inc.)
Introduction to luminescence
dosimetry
EXPOSURE
Radiation
\
Radiation sensor
(insulating crystal)
Introduction to luminescence
d i t
dosimetry
STORAGE
Introduction to luminescence
d i t
dosimetry
READOUT
Light emission
(e.g., blue, UV)
Thermal
stimulation
ti l ti
(heating)
Introduction to luminescence
d i t
dosimetry
READOUT
Light
stimulation
(e.g., green)
Light emission
(e.g., blue, UV)
Introduction to luminescence
d i t
dosimetry
READOUT
Optically Stimulated
Luminescence detectors
(OSLD )
(OSLDs):
Al2O3:C (TLD500)
Thermoluminescence detectors
(TLDs):
LiF:Mg,Ti, CaF2
Light
stimulation
(e.g., green)
Thermal
stimulation
ti l ti
(heating)
Light emission
(e.g., blue, UV)
OSL readout system
Light source
PMT
Detection filters
Stimulation
filters
OSL
Dosimeter
(OSLD)
Methods of OSL stimulation
• CW-OSL ((continuous wave OSL))
• POSL (pulsed
( ls d OSL)
• LM-OSL (linearly modulated OSL)
CWCW
-OSL readout method
CW
W-OSL (a
arbitratry u
units)
400
300
constant
200
100
0
0
100
200
300
Time (s)
400
500
600
Stimulatio
on intensity
POSL readout method
0
50
100
150
200
250
300
350
400
450
500
550
0
50
100
150
200
250
300
350
400
450
500
550
Gate S
State
on
off
Time (s)
Commercial OSL dosimetry systems
(L d
(Landauer
I
Inc.))
InLightTM
• One manufacturer
MicroStarTM
• Two types of readers
• CW- stimulation readout
• Detectors
D t t
from
f
L
Landauer
d
Inc. only
www.Landauer.com, www.osldosimetry.com
OSL dosimeters
Dot
nanoDot
Characteristics of Al2O3:C OSLDs
for radiotherapy applications
Ideal detector
•Small size
•Good reproducibility
•None
None or well defined environmental corrections
•Dose linearity
•Dose
D
rate
t independence
i d
d
•Energy independence
•No directional dependence -isotropic response to
radiation
OSLD reproducibility
40
35
% number
30
25
20
15
10
5
0
0.94
0.96
0.98
1.00
1.02
1.04
Relative sensitivity
y
Courtesy of C. Yahnke
1.06
1.08
Environmental corrections
Temperature dependence
• During irradiation
• During readout
OSL temperature dependence
during irradiation
Jursinic, Med. Phys. 34(12), 4594-4604, 2007
Temperature effect during OSL
stimulation
ti l ti ((readout)
d t)
Andersen et al, Radiation Measurements, 43, 948 – 9532008
OSLD dose linearity, 6 MV
1200
Rdg
g (arbitrary
y units)
1000
800
600
400
200
0
0
100
200
300
400
Dose / cGy
Viamonte et al Med. Phys. 35(4), 1261-6, 2008
500
OSL dose supralinearity at
hi h doses
higher
d
Schembri V and Heijmen BJM. Med. Phys. 2007; 34:2113-2118.
DoseDose
-rate dependence
6 MV
Viamonte et al Med. Phys. 35(4), 1261-6, 2008
Absorbed dose energy dependence
f(Q) for Al2O3:C and LiF TLD
Energy
60Co
gamma rays
Mean Energy
(keV)
Q
F
Al 2O3 Co
Q
F
LiF Co
Ratio
Al 2 O3 /LiF
1250
1.000
1.000
1.00
50 kV X-rays
29
3.219 ± 0.3%
1.463
2.20
100 kV X-rays
60
2.861 ± 0.3%
1.376
2.08
150 kV X-rays
105
1.607 ± 0.3%
1.245
1.29
250 kV X-rays
170
1.449 ± 0.3%
1.192
1.19
6 MV X
X-rays
2020
0 990 ± 0.3%
0.990
0 3%
0 987
0.987
 1.00
1 00
10 MV X-rays
3050
0.983 ± 0.3%
0.976
 1.00
15 MV X-rays
4180
0.980 ± 0.3%
0.976
 1.00
25 MV X-rays
6600
0.973 ± 0.3%
0.976
 1.00
Mobit et al. Radiat Prot Dosim 119, 497-499, 2006).
Absorbed dose sensitivity
y relative
to 6 MV photons as a function of
beam quality for Al2O3:C
OSLD 60Co: Viamonte et al
2008, Reft, 2009
Jursinic, Med. Phys. 34(12), 4594-4604, 2007
Yukihara et al, Phys Med Biol 53,
R351-R379, 2008
OSL LET dependence
Yukihara et al. 2006
OSL LET dependence in carbon
beam
beam
Reft, Med. Phys. 36(5), 1690-9, 2009
Directional dependence
Jursinic, Med. Phys. 34(12), 4594-4604, 2007
Fading of OSL signal
1.2
Q(t))/Q(1min)
1.0
0 8
0.8
0.6
0.4
0.2
0
0
2
4
6
Time / min
Reft, Med. Phys. 36(5), 1690-9, 2009
8
10
12
Fading of signal with time
S ( t )  A  B  e  kt
Jursinic, Med. Phys. 34(12), 4594-4604, 2007
OSL dosimetry
Advantages
Ad
t
vs. disadvantages
di d
t
Advantages
•
•
•
•
•
•
•
Disadvantages
High sensitivity
• Sensitivity to light
High precision
• Non-tissue equivalent – energy
Size
d
dependence
d
Convenience
• Only 1 material currently
Readout flexibility
available (only 1 provider)
Fast non-destructive
Fast,
non destructive readout
Narrow stimulating beams may
could allow dose mapping
• No significant fading - dose
storage
• No need for annealing
• Although it can be bleached
and re-used if needed*
Clinical dosimetry applications
• In phantom
− PDD
− ROF
−IMRT QA
• In vivo
−external beam (entrance, exit dose)
−brachytherapy
60Co
relative output factor
Viamonte et al Med. Phys. 35(4), 1261-6, 2008
In vivo dosimetry
y
J Danzer* et al AAPM 2007
The small Al2O3:C
C crystals
M Aznar,
M.
Aznar Phys.
Phys Med.
Med Biol.
Biol 49,
49 1655
1655–69
69, 2004
courtesy of C. Andersen, Risø
Riso OSLOSL-optical fibre dosimetry
system
t
OSL   c  e  τt dt
OSL   c  e t dt
Both RL and OSL signals are seen
on the
th computer
t screen
M. Aznar, Phys. Med. Biol. 49, 1655–69, 2004
courtesy
t
off C
C. Andersen,
A d
Ri
Risø
In - vivo measurements for
a b
brachytherapy
h h
patient
• Cervix recurrence just above the vaginal wall
• Treated in 15 needles – OSL crystals in 2 needles
• 30 Gy delivered in 50 pulses over 50 hours
courtesy of C. Andersen, Risø
Stability of the Risø system
• OSL measured pulse dose between each pulse
• RL signal
g
integrated
g
to give
g
pulse
p
dose
• TPS with +/- 1 mm uncertainty
courtesy of C. Andersen, Risø
Remote dosimetry application
• Recently evaluated by Radiological Physics Center
(RPC) for remote dosimetry
y application
pp
• OSL dosimeters were irradiated in an acrylic minip
phantom
• Results indicated that the precision of OSL
dosimeters is comparable to that provided by
TLDs used for remote dosimetry
Summary
• OSLD have linear dose response and good
reproducibility (screened) for standard clinical doses
• Minimal energy dependence in megavoltage photon
beams
• Suitable
bl for
f accurate d
dosimetric measurements
– individual calibration factors
• Can
C b
be used
d in
i variety
i t of
f clinical
li i l applications
li ti
– surface dose detectors
– entrance
t
and
d exit
it dose
d
measurements
t
– brachytherapy
– dose mapping
• Are suitable for remote dosimetry
Acknowledgements
• Claus Andersen, Risø National Laboratory
• Cliff Yahnke, Landauer Inc.
Thank you
Energy dependence
Al2O3:C
water
Zeff=10.2
Zeff=7.2
LM-OSL arbitrary un
nits
LMLM
-OSL readout method
Time (s)