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