FRICKE AND ALANINE DOSIMETERS
Transcript of FRICKE AND ALANINE DOSIMETERS
FRICKE AND ALANINE DOSIMETERS
FRICKE AND ALANINE DOSIMETERSDOSIMETERSDOSIMETERS
Malcolm McEwen & Carl RossMalcolm McEwen & Carl Ross
Chemical dosimeters
In a chemical dosimeter the absorbed dose is d i d f i i h idetermined from some quantitative change in an appropriate material and any well-characterized chemical reaction may serve as the basis for the ydosimeter.
Fricke – the basicsFricke the basics
The chemical species of interest is the The chemical species of interest is the production of Ferric ions (Fe3+) from Ferrous ions (Fe2+) The Ferrous ions are in solution What is irradiated is therefore mainly water Ionizing radiation interacting with water Ionizing radiation interacting with water produces a range of ions, radicals and molecules:
H· OH· H2 H2O2 H+ OH- ‐aqe
Lots of products, therefore a lot of reactions
2 2H O HO
2 3Fe HO Fe HO 2 32 2Fe HO Fe HO
HO H H O 2 2 2HO H H O
2 32 2Fe H O Fe OH OH2 2
2 3Fe OH Fe OH
Note that O2is needed.
Dose range
Oxygen is the limiting factor, rather than the concentration of Fe2+
The maximum absorbed dose that can be measured is about 400 Gy.
g
Chemistry - preparationChemistry preparation
The Fricke solution consists of 1mM ferrous ammonium sulfate and 1mM sodium chloride in 0.4 M sulfuric acid.
Contaminants can significantly affect performance therefore care must be taken to clean all glassware carefully and to use high purity chemicals.chemicals.
Sodium chloride is added to reduce or eliminate any sensitivity to organic impurities.
Chemistry - preparationChemistry preparation
C t i t t d dContainment - standard
Teflon stopper
Lucite holder
Containment - specializedContainment specialized
Readout
0.6
Readout
0.4
0.5
0.6
ensi
ty0.2
0.3
0.4
Opt
ical
den
0.0
0.1
0.2
200 250 300 350 400Wavelength (nm)
0.0
Peaks at 224 nm and 303 nmCommercial spectrophotometers usually use both
Readout
10 0log ( / )OD I I c L
Readout
The yield of the Fe 3+ ion depends on the temperature of
10 0
the solution during irradiation (0.12% per degree C)
The molar extinction coefficient depends on the temperature of the solution during readouttemperature of the solution during readout
OD
F 3(Fe )OD
DG L
ReproducibilityReproducibility
Precision is typically better than 0.15 % yp yStability of the dosimeter response is only slightly worse.
Energy dependence – photon beamsEnergy dependence photon beams
Energy dependence – electron beams
1.015
Energy dependence electron beamsse
d 1.005
1.010
e3+),
norm
ali s
1.000
G(F
e
0.990
0.995
1999 2000 data
4 6 8 10 12 14 160.985
1999-2000 data2007 data
Es (MeV)
Measurement of dose
F 3(Fe )OD
DG L (Fe )G L
Dw = DF fw,F Pwall kdd
f(Q) = fw,F Pwall
Is Fricke a primary or secondary dosimeter?Is Fricke a primary or secondary dosimeter?
ODD
F 3(Fe )
DG L
A li ti t dApplications today
Fricke is disappearing from even primary standardsFricke is disappearing from even primary standards laboratories. Does it have a future?
Low energy electron beam dosimetry
Ir-192 dosimetry Ir 192 dosimetry
Alanine – the basicsAlanine the basics
Alanine - developmentAlanine development
Major players:Major players:NISTNPLNPL
Latecomers:NRCPTB
Alanine pelletsAlanine pellets
Major players:Major players:NISTNPLNPL
Alanine – readout
Alanine – readout
Signal ExtractionSignal Extraction
HoldersHolders
LinearityLinearity
Relative absorbed dose sensitivityRelative absorbed dose sensitivity
MV photon beams
o-60
1.005
p
rela
tive
to C
o
1.000
ater
resp
onse
0.990
0.995
ne d
ose-
to-w
a
0.985 Sharpe and Sephton (2006)Zeng et al (2004)Bergstrand et al (2003)A t t l (2008)
TPR20,10
0.55 0.60 0.65 0.70 0.75 0.80 0.85
Alan
in
0.980
Anton et al (2008)
MV photon beams
1.005Meas rement
p
1.000
pons
eMeasurement
Monte Carlo
0 990
0.995
ativ
e re
sp
0.985
0.990rela
55 60 65 70 75 80 85
%dd(10)x
Electron beams
Relative absorbed-dose response
(electrons/60Co)Standard uncertainty
(electrons/ Co)
Bergstrand et al (2004) 0.971 0.015
Zeng et al (2005) 0.987 0.011
McEwen et al (2006) 0.986 0.012
Electron beams
1.005
0.995
se to
60C
o
0.985
ve re
spon
s
0.965
0.975
rela
tiv
Measurement
Monte Carlo0.965
5 10 15 20 25nominal energy (MeV)
kilovoltage
1.2
kilovoltage
e to
60C
o
1.0
1.1
spon
se re
lativ
0.8
0.9
Air
kerm
a re
s
0 5
0.6
0.7
Regulla and Deffner (1982)Zeng and McCaffrey (2005)
Eav (MeV)
0.01 0.1 1 100.4
0.5
av ( )
Applications - uncertaintiesComponent Standard Uncertainty (10 Gy)
1. Calibration in 60Co
60Co primary standard realization of dose 0 2 % - 0 4 %Co primary standard realization of dose 0.2 % 0.4 %
Irradiation temperature 0.05%
Average mass of 4-6 pellets 0.05%
Precision, set of 4-6 alanine pellets 0.1 % - 0.2 %
Overall (Calibration) 0.2 % - 0.5 %
2 M d i lt b2. Measure dose in megavoltage beam
Calibration reference 0.2 % - 0.5 %
Irradiation temperature 0.1%
Average mass of 4-6 pellets 0 05%Average mass of 4-6 pellets 0.05%
Precision, set of 4-6 alanine pellets 0.2 % - 0.3 %
Inter-pellet variations 0.3 % - 0.5 %
Correction for energy dependence (MVphotons) 0.2%photons)
Overall (Measurement of dose) 0.5 % - 0.8 %
Applications (I) - auditpp ( )
Applications (I) - auditpp ( )
D i d Dosimeters and phantom can be mailed Useful as part off commissioning processprocess Also used in UK dose audits
Audit - resultsAudit results
Applications (II) – Tomotherapy pp ( ) py
ProtocolProtocol
Results
Applications (III) – electron depth dose pp ( ) p
SummarySummary
Alanine and Fricke are unlikely to feature much in clinical Alanine and Fricke are unlikely to feature much in clinical dosimetry
However, they are well-established systems and have y yunique properties applicable to special situations
Keep them in mind, they could be useful one day!p , y y
AcknowledgementsAcknowledgementsc o edge e tsc o edge e ts
Gerhard Stucki – METAS
Ge Zeng – ex NRC
Simon Duane, Peter Sharpe – NPL