GlD i tGel Dosimetry - American Association of … i tGel Dosimetry L..Jo Sc e e d Od g John...

G l D i tGel Dosimetry L. John Schreiner and Tim Olding . Jo Sc e e d O d gCancer Centre of Southeastern Ontario

Queen’s University

DisclosureDisclosure

Schreiner, AAPM Colorado ‘09

Learning objectives

Introduce gel dosimetry

g j

• Introduce dosimeter systems• Readout systemsReadout systems• Fundamental mechanisms

Di li i l li iDiscuss clinical application• Preparation and Use • Show some examples of use


Wh t is l d sim t r?What is a gel dosimeter?


What is a gel dosimeter?

89 % bulk waterh 89 % bulk waterh

Small amount stuff 5 % gelatinSmall amount stuffthat changes under

irradiation

5 % gelatin


irradiation

What is a Fricke gel dosimeter ?


5 % gelatinFe2+

F 3+ 5 % gelatinFe3+

(in FX gels, + 0.05 mM xylenol orange)


What is a polymer gel dosimeter ?


monomers

5 % gelatin

monomers

l 5 % gelatinLarge polymers(in normoxic gels, + 5 mM tetrakis THPC)


What is a gel dosimeter ?

hhChanges can be monitored by variousChanges can be monitored by various techniques and dose mapped in three dimensions

Small amount stuff

dimensions

Small amount stuffthat changes under

irradiation


irradiation

So a gel dosimeter is a d system to capture dose

information in 3D

Yves DeDeene Ghent

CCSEO


Schreiner, AAPM Colorado ‘09c/o Andrew Jirasek, U. Victoria, BC

Intrinsic energy dependence :Most investigations of polymer gels in proton

beams indicate the gels exhibit an LET dependencep

Schreiner, AAPM Colorado ‘09c/o Andrew Jirasek, U. Victoria, BC

Gel dosimetry


Parker MSc 1997

Gel DosimetryyNot yet clinically adopted broadly

• Imaging for readout not always readily available (particularly the goldavailable (particularly the gold standard, MRI)

• Gel preparation (toxicity, oxygen contamination )contamination …)

• May have better tools for applicationsMay have better tools for applications tested to date

Dose Quantification

• Looking at the MR relationship gives a sense of the parameters defining the dose of the parameters defining the dose relationship


• With substitution R1 = 1/T1

A busy slide: why we use calibrations


Typical dose response


MRIBased on change of NMR spin-relaxation rates in irradiated

dosimeter

Fricke gels R1 ( = 1/T1 )• Fricke gels - R1 ( = 1/T1 ) • polymer gels – R2 (= 1/T2 ) or magnetization transfer imaging

Schieb 2001 BANG gel Crooks 1994 Fricke gel

AsideWhat is the accuracy and precision of gel dosimetry

• Relative doses - 3%, <2% easily in our workDelivered dose (absolute dose) 5% easily 3% with some work• Delivered dose (absolute dose) – 5% easily, 3% with some work

Schieb 2001 BANG gel Crooks 1994 Fricke gel

x-ray CT Based on change of density in irradiatedpolymer gel dosimeters

ypolymer gel dosimeters

Hilts et al. PMB 2000 PAGNIPAM with glycerol

PAG

Jirasek et al PMB 2009Jirasek et al. PMB 2009

B d h f ti l tt tiOptical CT

Based on change of optical attenuation coefficients in irradiated dosimeter

• Fricke gels - Absorption changes

p

g p g

• polymer gels – mainly changes in scatter

Optical CT Modus Medical CBCT optical systemp

FX gelFX gel

Optical CT0.15

m-1

)p0.1

uatio

n (c

m

5 cm9 cm

0

0.05

Atte

nu

2 cm

00 50 100

Position (mm)0.4-1

)

y = 0.9213x

0.3

Coe

ffici

ent (

cm-

0.1

0.2

sta

Atte

nuat

ion

Uncorrected Scatter SolutionsBSA CorrectedDye SolutionsFan BeamLi Fit (BSA C t d)

CBCT optical system

00 0.2 0.4 0.6 0.8 1 1.2

Spectrophotometer Attenuation Coefficient (cm-1)

Vis Linear Fit (BSA Corrected)

Timescale for Gel dosimetry (typical times and limits)

Prepare IrradiateFricke

Wait( bring to

r dnFricke systems

45 minNIPAM (polymer)

Fricke<20 minPolymer

12 hrs to 1 weekPolymer

12 hrs to 1 week

radn

room T )

45 minym

No limit( dark cool storage )

3 4 hAnalysis Readout

Fricke

Wait

3-4 hrsCalibration, registration,

l i (

OpticalCBCT < 8 +10 min

2nd gen CT > 30 min 1 hrMRI

30 min – 2 hour (maybe )Polymer

> 12 (24) hrsanalysis (gamma maps DVHs etc)

MRI30 min 1 hr f (readout)

( MRI may be more sensitive )



Wait( bring to

r dnFricke systems




12 hrs to 1 week

radn

room T )

45 minym



Fricke

Wait


l i (


> 12 (24) hrsanalysis (gamma maps DVhs etc) f (readout)

( MRI may be more sensitive )NIPAM added at too high T



Wait( bring to

r dnFricke systems




12 hrs to 1 week

radn

room T )

45 minym


( dark cool storage )


Fricke

Waitstorage )


l i (


2nd gen CT > 30 min 1 hrMRI


> 12 (24) hrsanalysis (gamma maps DVhs etc)

MRI30 min 1 hr f (readout)




Wait( bring to

r dn• Calibration Fricke systems




12 hrs to 1 week

radn

room T )

• Choice of gel and readout system45 min

ymNo limit( dark cool

storage )

g y

3 4 hAnalysis

Fricke

WaitReadout


l i (


> 12 (24) hrs


2nd gen CT > 30 min - 1 hrMRI

( bring to measurement

room T )analysis (gamma maps DVHs etc) f (readout)


MRI30 min / 1 hr

room T )

CALIBRATION

vialsInternal

vials

Independent from same batch

Gel Dosimetryy

Will i s li ti s llWill now review some applications wellsuited to gels


Application 1: Beam commissioning of small fieldssmall fields

Moutsatsos et al., Dosgel’08

Pappas et al., Dosgel’08

Petrokokkinos et al., D l’08Dosgel’08

Application 2: Commissioning of t h i i th li i

Fricke Gel IMRT Validation

new techniques in the clinic

Fricke Gel IMRT Validation


200 cGy Eclipse Plan OptCT Measurement

IMRT Gamma Evaluation

Gamma 3% 3mm

(93% of dosimeter i l d)pixels passed)


Application 2b: Commissioning of new techniquestechniques

Ceberg et al., Dosgel’08

PAGAT gel dosimeter with MRIPAGAT gel dosimeter with MRI readout at 1.5 T using multiecho T2 sequence (TE 25 ms, TR 4000 ms) ,

3voxel size 1x1x3 mm3


Application 3: Adaptive Radiation Therapy Process QATherapy Process QA

A proposalA proposal


Image Guided Ad ti R di ti


Adaptive Radiation Therapy

1) These are all intricate processes with complex data transfer between points, also requirin human evaluation and human


also requiring human evaluation and human intervention.

Could use a test tool that mimics a patient undergoing treatment

5 & 65 & 6


8

Physicists / physics team / rad oncs

4

90

2

Dose (Gy)

EvaluationSchreiner, AAPM Colorado ‘09

Evaluation

Jar Volume

100 EclipseGel

Bladder

100Example con’t

25

50

75

Frac

tion

of V

olum

e (%

) Gel

25

50

75

Frac

tion

of V

olum

e (%

)

00 2 4 6

Dose (Gy)

00 2 4 6

Dose (Gy) Rectum

100

%)

Prostate

100

%)

0

25

50

75

Frac

tion

of V

olum

e (%

0

25

50

75

Frac

tion

of V

olum

e (%

00 2 4 6

Dose (Gy)

00 2 4 6

Dose (Gy) Prostate + 1.5cm (Control Volume)

75

100m

e (%

)Cumulative GVH

0

25

50

0 2 4 6

Frac

tion

of V

olum

(gamma test)


Dose (Gy)

Jar Volume

100 EclipseGel

Bladder

100Example con’t

25

50

75

Frac

tion

of V

olum

e (%

) Gel

25

50

75

Frac

tion

of V

olum

e (%

)

00 2 4 6

Dose (Gy)

00 2 4 6

Dose (Gy) Rectum

100

%)

Prostate

100

%) OOPs

0

25

50

75

Frac

tion

of V

olum

e (%

0

25

50

75

Frac

tion

of V

olum

e (% OOPs

00 2 4 6

Dose (Gy)

00 2 4 6

Dose (Gy) Prostate + 1.5cm (Control Volume)

75

100m

e (%

)Cumulative GVH

0

25

50

0 2 4 6

Frac

tion

of V

olum

(gamma test)


Dose (Gy)

Conclusions• Many of the problems that have kept gel dosimetry

out of the clinic have been corrected

• Gels have some special roles:p– Small beam commissioning

Validation of new techniques (particularly before using– Validation of new techniques (particularly before using and external credentialing service, e.g., RPC)

P h h i l i RT P QA• Perhaps have a unique role in RT Process QA


ConclusionsConclusions

C d i• Care and consistency


Ideal Dosimeter: makes for well planned, smooth and easy route to a l d d ti tiplanned destination.

Clinical Dosimeters: trip may not be as smooth and may require a bit more skill but with careful use of skills and technique destination can be reached.


DosGel Conferences on Radiotherapy Gel DosimetryDosimetry.

(2004, 06 and 08 proceedings available on web through J Phys Conf Series)J Phys Conf Series)

Acknowledgementsg• Graduate Students: (current and long previous)

Matthew Podgorsak, Chantal Audet, Brian Keller, WillMatthew Podgorsak, Chantal Audet, Brian Keller, Will Parker, Rob Senden, Adrian Fuxman, Valeria Koeva, Oliver Holmes, Tim Olding,

• Dosgelers: Kim McAuley, Simon Doran, Geoff Ibbott, Yves Dedeene, Mark Oldham, Evangelos Pappas, Thomas Maris, Sophie Ceberg, Michele Hilts, Sven Bäck, Andrew Jirasek, Clive Baldock and othersAndrew Jirasek, Clive Baldock and others


GlD i tGel Dosimetry - American Association of … i tGel Dosimetry L..Jo Sc e e d Od g John...

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