TG 51 Outline - American Association of Physicists in Medicine … · 2009-07-01 · AAPM’s...

TG 51TG 51

M S if l H PhM. Saiful Huq, PhDepartment of R

University of PittsbUniversity of PittsbPittsb

2009 AAPM2009 AAPM2009 AAPM2009 AAPM

1 Outline1 Outline

h D FAAPM FInstPh.D., FAAPM, FInstPRadiation Oncologyburgh Cancer Instituteburgh Cancer Instituteburgh, PA

M S S h lM S S h lM Summer SchoolM Summer School

ObjObjObjecObjec

• Implementation of TG

TG 51 CTG 51 CThe PhyThe PhyThe PhyThe Phy

titictivective

-51 protocol in the clinic

Clinical issues: Dave FollowillClinical issues: Dave Followillysics of TG 51: Dave Rogersysics of TG 51: Dave Rogersysics of TG 51 Dave Rogersysics of TG 51 Dave Rogers

OutlOutl

• Background• Describe the basic e• Describe the basic e• Step-by-step proced

electron beam calibr• What to do with new• Errors in TG-51• Conclusions• Conclusions

ineine

quations in TG 51quations in TG-51dures for photon and ation

w chambers

1969-71

N b dNX-basedSCRAD

N

T

AAPM Protocols for RadiotDosimetryDosimetry

1983 1999

NX-basedAAPM

N b d

AAPMTG-21

ND,w-basedAAPMTG-51herapy

AAPM’s TGAAPM’s TG--51 Prot51 ProtPhoton and EPhoton and EPhoton and EPhoton and E

Peter R. AlmondPeter J. BiggsggB.M. Coursey W.F. Hanson

Med. Phys. 26 18

tocol for Hightocol for High--Energy Energy Electron BeamsElectron BeamsElectron BeamsElectron Beams

d, ChairmanM. Saiful Huq qRavinder NathD.W.O. Rogers

847-1870 (1999)

Summary Summary -- PhPhQw MkD

2 2 :: ADCL ADCL Co60

DN

1. Select chamber1. Select chamber

2. 2. :: ADCL ADCL w,DN

Qk3.3. vsvs Q Q :: Measure BQ Measure BQ

hoton Beamshoton BeamsCowDQ N 60

,

4. Measure M4. Measure M

Summary Summary -- EleEle

1 Select chamber1 Select chamber

Qgr

Qw kMPD

2. 2. :: ADCL ADCL Co60

w,DN

1. Select chamber1. Select chamber

4.4. vsvs RR50 50 :: Measure BQMeasure BQ50Rk

3.3. : Table lookup: Table lookupecalk

50R

ectron Beamsectron BeamsCo

50

60w,DecalR Nkk

5. Measure 5. Measure QgrP

Q Q 6. Measure M6. Measure M

The Simplicity of the The Simplicity of the NThe Simplicity of the The Simplicity of the N

• For a known QN• For a known

Q

Qw,DN

Qw MD

• At any user quality

Qw MkD

N based Formalismbased FormalismND,w --based Formalismbased Formalism

QQw,DMN

y Q:

CowDQ N 60

,Q ,

Beam QualBeam Qual

Co

QwD

Q NN

k 60, CowD

Q N 60,

•• Should be measured direcShould be measured directhe same quality as the userthe same quality as the userthe same quality as the userthe same quality as the user•• But.... only a few PSDLs cBut.... only a few PSDLs c

lity Factorlity Factor

CoQ

Qw

MDMD

60 //

CoCo

w MD 6060 /

ctly for the user ion chamber, at ctly for the user ion chamber, at , Q, Q, Q, Qcan perform such measurementscan perform such measurements

Theoretical DetTheoretical Det

w

PL

w

w

waair

Q

PL

PL

k

w

air

• Valid for all types• Most common pracMost common prac

termination of termination of kkQQ

PPP

celflgrwall

Qcelflgrall

PPP

PPP

Co

celflgrwall60

of high-energy beamsctice todayctice today

TGTG 51 Equa51 EquaTGTG--51 Equa51 Equa

QDQwD

ations for ations for ations for ations for

QQw

Photon Beams

Qw MD

Electron Beams

QQ MPD grw MPD

CowDQ NMk 60

,

CoDlR

Q Nkk 60 wDecalRr Nkk ,50

kkQQkkQQ

PhotonPhoton--electron electron

w

walw

airecal

L

PL

k

wair

PL

QQecal (R(R50 ==QQecal (R(R50

Conversion FactorConversion Factor

Qecalcelflll PP

Cocelflgrwall PPP

60

= 7.5 cm)= 7.5 cm) 7.5 cm) 7.5 cm)

Electron Quality Electron Quality

w

PL

w

waair

RPL

PL

k

50

air

QQecal (R(R50 ==

Conversion Factor Conversion Factor

PP

celflwall

Rcelflall

PPP

PP50

Qecal

f

= 7.5 cm)= 7.5 cm)

StepStep--byby--step Procstep ProcStepStep--byby--step Procstep ProcImplementation oImplementation o

Photon B

cedures for Clinical cedures for Clinical cedures for Clinical cedures for Clinical of TGof TG--51 protocol51 protocol

Beams

Reference DReference D

Photon Be

Reference DReference D

Photon Be

Qw MkD

Dosimetry Dosimetry

eams

Dosimetry Dosimetry

eams

CowDQ N 60

,

PhotoPhoto

Obt i lib ti CoN 60• Obtain an calibration c

• Stability check measurements

Cow,DN 60

Stability check measurements

• must be traceable to nbs b d d s t t

Cow,DN 60

absorbed dose-to-water

onsons

ffi i t f i i ti h bcoefficient for ionization chamber

s before and after the calibrations before and after the calibration

ational primary standards of

CalibrationCalibrationCalibrationCalibration

CowDN 60

6060CoCowD,

waterwaterwaterwater

CowD60

Cavity centered at theCavity centered at the

w

n Laboratoryn Laboratoryn Laboratoryn LaboratoryCo

wD60

6060CoCoCoM 60

ddddrefref


CoM 60

e reference depth e reference depth ddrefref

User Beam Quality User Beam Quality DeptDept

Cavity centCavity centQQ

Cavity centCavity cent


rawM

corrected for rawM

Q: at the Reference Q: at the Reference h h ddth th ddrefref

tered at tered at dd ff

QQtered at tered at ddrefref

dd ffddrefref


QwD

influence quantities

Point of MePoint of Me

ddddrefref

ddccPPeffeff

P of a cyl-chamber is posPeff of a cyl-chamber is posmeasurement: a distance dc0.6 rcyl for photons and 0.5

For a pp-chamber Peff is in t

easurementeasurement

: use of Pgrwindow thickness window thickness

1 1 f gr

: use of Peff

1 mm1 mm

u f eff

dd

PPeffeff

sitioned upstream of the point of

ddrefref

sitioned upstream of the point of dc equal to

rcyl for electrons

the front of the cavity.

M tM tMeasurementMeasurementt f Cht f Chts of Chargets of Charge

PhantomPhantomPhantomPhantom

Must be performed in a Must be performed in a water phantomwater phantompp

Plastic or water equivalent Plastic or water equivalent plastic not allowed

mmmm

waterwater

plasticplasticplasticplastic

Chamber WatChamber Wat

Waterproof chamber: ideaWaterproof chamber: idea Waterproof chamber: ideaWaterproof chamber: idea

PMMA sleeve PMMA sleeve 1 mm in th1 mm in thsleevesleeve

h h b h h b Air gap near the chamberAir gap near the chamber

terproofingterproofingp gp g

alalalal

hickness or thin latex rubber hickness or thin latex rubber

ll ll 0 0 wall wall 0.2 mm0.2 mm

Corrections to CCorrections to CCorrections to CCorrections to C

TPion PPPM TPion

Charge ReadingCharge ReadingCharge ReadingCharge Reading

rawpolelec MPP rawpolelec

Temperature and PrTemperature and PrTemperature and PrTemperature and Pr

2.273(p TP 2.273(2.273(

ressure Correctionressure Correctionressure Correctionressure Correction

T 33.101)P

T 33.101)22

)

Polarity CoPolarity Co

rawMP

polP2

The signs of The signs of MMrawraw MUMU

Allow adequate time aAllow adequate time a

orrectionorrection

raww M rawM2

STST be usedbe used

after reversing polarityafter reversing polarity

RecombinatioRecombinatio

Two voltage method: Two voltage method: M

HionM

VP

MM

on Correctionon Correction

(V (VHH) and (V) and (VLL))HrawM L

rawM

HV1

HHraw

L

H

VMV

1

L

HLraw

rawVV

MM

Electrometer CoElectrometer Co

if chamber and electif chamber and elect001.Pelec

NonNon--unity if chamber and elecunity if chamber and elecseparatelyseparately

orrection Factororrection Factor

trometer are calibrated as a unittrometer are calibrated as a unit

ctrometer are calibrated ctrometer are calibrated

Practical ConsiPractical Consi

Verify the stability of the Verify the stability of the V fy y fV fy y f

Check the integrity of the Check the integrity of the

Allow enough time for the Allow enough time for the equilibriumequilibriumequilibriumequilibrium

iderationsiderations

dosimeter system dosimeter systemm y mm y m

waterproofing sleeve waterproofing sleeve

dosimeter to reach thermal dosimeter to reach thermal

Practical ConsPractical Cons

PrePre--irradiate chamber with 2irradiate chamber with 2--equilibrium in the different maequilibrium in the different ma

Aft it hi l it lAft it hi l it l After switching polarity or polAfter switching polarity or polso that chamber’s reading reacso that chamber’s reading reac

Leakage current (should be insLeakage current (should be ins

siderationssiderations

5 Gy to achieve charge 5 Gy to achieve charge aterialsaterials

l i i lt ll h ti l i i lt ll h ti larizing voltage allow enough time larizing voltage allow enough time ches equilibriumches equilibrium

significant)significant)

Measurements oMeasurements o

Need to measure BQ becauseNeed to measure BQ because

N m u Q uN m u Q u

w

w

w

airQ

L

PL

k

airPL

of Beam Qualityof Beam Quality

e e kQ is given a function of BQis given a function of BQ

Q g fu f Qg fu f Q

Qcelflgrwall PPP

Cocelflgrwall PPPP

60

Beam Quality SBeam Quality S

PhPh

Beam Quality SBeam Quality S

PhotoPhoto

• Percentage depth dose ato photons only (i.e., exccontamination) Q= %Q= %dddd((

C l h b hif PDI

contamination), Q= %Q= %dddd((

• Cyl chambers: shift PDI

• PP chambers: no shift n

SpecificationsSpecificationsSpecificationsSpecifications

onsons

at 10 cm depth in water due cluding electron

dd(10)(10)XX

I b 0 6

dd(10)(10)XX

I curve by 0.6rcav upstream

needed

Photon 0.6rPhoton 0.6rPhoton 0.6rPhoton 0.6r

Dave RogersDave Rogers

rrcavcav DepthDepth--shiftshiftrrcavcav DepthDepth shiftshift

Measurement of Photon Measurement of Photon

MUSTMUST be be measured usingmeasured using

1 mm 1 mm PbPb Filter 10MV Filter 10MV or higheror higher

10 cm x 10 cm

or higheror higher

10 cm x 10 cm

Beam Quality, Beam Quality, %%dddd(10)(10)XX

SSD=100 cm

Electron ConElectron Con

headhead

variable evariable e--


ntaminationntamination

1 mm lead1 mm leadheadhead

removes removes variable evariable e--

adds known eadds known e--

L d F il CL d F il CLead Foil CLead Foil C

The 1 mm The 1 mm PbPb filter removes thfilter removes th The 1 mm The 1 mm PbPb filter removes thfilter removes thhead of the machinehead of the machine

Correct the effects of electrCorrect the effects of electrfilter usingfilter using

%dd(10)x = [0.8905+ 0.00

f il t 50 5foil at 50 5cm

use values of %use values of %dddd(10)(10)pbpb and and NN

C tiC tiCorrectionCorrection

he electrons generated in the he electrons generated in the he electrons generated in the he electrons generated in the

rons generated in the lead rons generated in the lead gg

0150%dd(10)pb]%dd(10)pb

%dd(10) b 73%m , %dd(10)pb 73%

NOTNOT fractional depth dosefractional depth dose

kkQQ for Cylfor Cyl


indrical Chambersindrical Chambers

ReferencReferenc

Pb Filter

REMOVE

Reference conditionsReference conditions

•• Depth: 10 g cmDepth: 10 g cm--22

•• FS:FS: 10 x 10 cm10 x 10 cm--22

•• SSD or SADSSD or SAD

e Dosimetrye Dosimetry

Dose atDose atDose atDose at

•• SSD setups: use clinical PSSD setups: use clinical Pat at ddrefref to that to that ddmaxmax

•• SAD setups: use clinical SAD setups: use clinical

t t ddmaxmaxt t ddmaxmax

PDD curve to convert dose PDD curve to convert dose

TMR curvesTMR curves

S S PhPhSummary Summary -- PhotonsPhotons

Get traceable

M %dd(10)

N

Measure %dd(10)

Determine %dd(1(

Look up Look up kQ for yfor y

Measure Mraw at

M= Pi PTP P l P M= Pion PTP Pelec Pp

CQ k 60 CowDQ

Qw NMkD 60

,

) ith l d f il

Cow,DN60

) with lead foil

10)x)x

your chamberyour chamber

10 g cm-2

l Mpol Mraw

StepStep--byby--step procstep procImplementation ofImplementation ofImplementation ofImplementation of

ElectElect

cedures for Clinical cedures for Clinical f TGf TG 51 protocol:51 protocol:f TGf TG--51 protocol:51 protocol:tronstrons

ReferenceReference

Electron

ReferenceReference

Electron

QQ kMPD Qgr

Qw kMPD

kkkk


n Beams


n Beams

CoNk 60 CowDecalR Nk ,50

kkkkQQ

Measurements oMeasurements o

N d BQ bN d BQ bNeed to measure BQ becauseNeed to measure BQ because

waw

airPL

w

air

RPL

k

50

of Beam Qualityof Beam Quality

k’ i i f i f BQi i f i f BQe e k’R50 is given a function of BQis given a function of BQ

Rcelflall PP

0

Qecalcelflwall

R

PPP

50

Beam Quality SBeam Quality SBeam Quality SBeam Quality S

Electro

• Half-value depth R50

• Depth in water at which thits value at the absorbed dits value at the absorbed d

•• CylCyl chambers: shift PDI cchambers: shift PDI c

•• PP chambers: no shift neePP chambers: no shift nee

SpecificationsSpecificationsSpecificationsSpecifications

ons

he absorbed dose is 50% of dose maximumdose maximum

urve by 0.5rurve by 0.5rcavcav upstreamupstream

dedded

Measurement of ElectrMeasurement of Electr

MUSTMUST be measured be measured usingusing

FS 10 10 2

us ngus ng

FS 10 x 10 cm-2

20 x 20 cm-2 or

for Rfor R5050 8.5 cm

ron Beam Quality, ron Beam Quality, RR5050

SSD=100 cm

Electron BElectron BElectron BElectron B


Beam QualityBeam QualityBeam QualityBeam Quality

DeterminatioDeterminatio

R50 = 1.029 I50 -for

R = 1 059 IR50 = 1.059 I50 -for I

on of on of RR5050

0.06 cm r 2 I50 10 cm

0 37 cm- 0.37 cm I50 10 cm

kk´́RR5050 for Cylfor CylRR5050yy


lindrical Chamberslindrical Chambers

kk´́RR5050 for for RR5050


pp Chambers pp Chamberspppp

Chamber & PhantChamber & PhantChamber & PhantChamber & Phant

l t only water phantoms

no cyl-chambers

pp-chambers only

6 MeR 2 5 R50 2.5 g

tom Requirementstom Requirementstom Requirementstom Requirements

only water phantoms

cyl & pp-chambers y pprecommended

EnergyV/ m2g/cm2

ReferenceReference

RefRef

dref = 0.6 R

• close to dmax fmax f

• deeper than d

e Conditionse Conditions

depthdepth

R50 - 0.1 (cm)

for Eo<10MeVf o

dmax for higher Eo

ReferenceReference

Field size (at the phanto 10 cm x 10 cm for R50

20 20 f R 20 cm x 20 cm for R50

SSD: clinically used

e Conditionse Conditions

om surface):0 8.5 cm

8 5 0 8.5 cmd

QQgrP

Depends on the user’s beamDepends on the user’s beam Point of Measurement at rePoint of Measurement at rePoint of Measurement at rePoint of Measurement at re =1 for plane=1 for plane--parallel chparallel ch for cylindrical chambers:for cylindrical chambers:

QgrP

rawQ dMP

Qgr M

P

m and must be measured clinicallym and must be measured clinicallyef depthef depthef depthef depthhambershambers

cavref r.d 50 refraw

f

d

Use of PlaneUse of Plane--papa

Cross CalCross Cal

ppCo

wDecal Nk 60,

rallel Chambersrallel Chambers

librationlibration

cylCQ 60 pp

R

cylCowDecalR

Qgr

kM

NkkMP

50

60,50

50

Subsequent Use of Subsequent Use of Subsequent Use of Subsequent Use of Chamber in an EChamber in an E

ppQ RppQ

w kMD 50

the Crossthe Cross calibrated calibrated the Crossthe Cross--calibrated calibrated Electron Beam QElectron Beam Q

ppC60 ppCowDecal Nk 60

,

Summary Summary --

•• Get traceable Cow,DN60

Measure I50 and dete

Determine dref = 0.6R

M M t d Measure Mraw at dref

M= P P P P M M= Pion PTP Pelec Ppol Mr

ElectronsElectrons

ermine R50

R50 - 0.1 cm

aw

Summary Summary --

Look up kecal for your c

Determine 50Rk

Measure (if cyl QgrP

RQ

grQw kMPD 5

ElectronsElectrons

hamber

chamber is used)

CowDecal Nk 60

,50

Dose at Dose at

•• Determine dose at Determine dose at dref

•• Divide dose at Divide dose at dref by the fractby the fract

•• Use clinical PDD curve to deterUse clinical PDD curve to deter•• Use clinical PDD curve to deterUse clinical PDD curve to deter

•• Use TGUse TG--25 recommendations an25 recommendations anPhys Phys 2323 383383 388 (1996)]388 (1996)] for wafor waPhys Phys 2323 383383--388 (1996)]388 (1996)] for wafor wafor converting PDI curve to PDDfor converting PDI curve to PDD

ddmaxmax

tional depth dose at tional depth dose at dref

mine fractional depth dose at mine fractional depth dose at dmine fractional depth dose at mine fractional depth dose at dref

nd the eq. of Burns et al nd the eq. of Burns et al [Med [Med aterater toto air stopping power ratios air stopping power ratios aterater--toto--air stopping power ratios air stopping power ratios D curveD curve

What To Do With ChaWhat To Do With ChaWhat To Do With ChaWhat To Do With Chain the Prin the Pr

• Find the closest matching cham

• The critical features are in ordof the air cavity, the presencey, pwall thickness

ambers Not Included ambers Not Included ambers Not Included ambers Not Included rotocol?rotocol?

mber for which data is given

der: the wall material, the radius of the central electrode, and the ,

What To Do With ChaWhat To Do With Chain the Prin the Pr

• As long as the wall material isshould be accurate to within 0

• It is your responsibility to coresults to those of a calibrategiven

ambers Not Included ambers Not Included rotocol?rotocol?

s matched, these matching data 0.5%

onfirm this by comparing the ed cyl chamber for which data is y

EEErrorError

• Fig. 5: PR06G curve appearcorrect curve is the lower b l t th belongs to the group repreNE2581, PR06G

rsrs

rs twice on this curve. The curve, i.e. the curve that

t d b NE2561 N23331 sented by NE2561, N23331,

EEErrorError

• Worksheet A: Item 8a is squared symbol in the equPion is correct in the text

rsrs

missing 2 brackets and a uation for Pion but eq. 11 for

ConclusiConclusiConclusiConclusi

• TG-51 simplifies clinical refe

• It also improves the accuracIt also improves the accuracdosimetry

ionsionsionsions

erence dosimetry

cy of clinical reference cy of clinical reference

TG 51 Outline - American Association of Physicists in Medicine … · 2009-07-01 · AAPM’s...

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Transcript of TG 51 Outline - American Association of Physicists in Medicine … · 2009-07-01 · AAPM’s...