TG 51 Outline - American Association of Physicists in Medicine … · 2009-07-01 · AAPM’s...
Transcript of TG 51 Outline - American Association of Physicists in Medicine … · 2009-07-01 · AAPM’s...
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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
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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
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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
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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
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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)
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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
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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
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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 ,
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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
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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
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TGTG 51 Equa51 EquaTGTG--51 Equa51 Equa
QDQwD
ations for ations for ations for ations for
QQw
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Photon Beams
Qw MD
Electron Beams
QQ MPD grw MPD
CowDQ NMk 60
,
CoDlR
Q Nkk 60 wDecalRr Nkk ,50
kkQQkkQQ
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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)
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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)
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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
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Reference DReference D
Photon Be
Reference DReference D
Photon Be
Qw MkD
Dosimetry Dosimetry
eams
Dosimetry Dosimetry
eams
CowDQ N 60
,
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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
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CalibrationCalibrationCalibrationCalibration
CowDN 60
6060CoCowD,
waterwaterwaterwater
CowD60
Cavity centered at theCavity centered at the
w
n Laboratoryn Laboratoryn Laboratoryn LaboratoryCo
wD60
6060CoCoCoM 60
ddddrefref
waterwaterwaterwater
CoM 60
e reference depth e reference depth ddrefref
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User Beam Quality User Beam Quality DeptDept
Cavity centCavity centQQ
Cavity centCavity cent
waterwaterwaterwater
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
waterwaterwaterwater
QwD
influence quantities
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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.
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M tM tMeasurementMeasurementt f Cht f Chts of Chargets of Charge
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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
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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
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Corrections to CCorrections to CCorrections to CCorrections to C
TPion PPPM TPion
Charge ReadingCharge ReadingCharge ReadingCharge Reading
rawpolelec MPP rawpolelec
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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
)
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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
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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
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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
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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
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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)
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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
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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
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Photon 0.6rPhoton 0.6rPhoton 0.6rPhoton 0.6r
Dave RogersDave Rogers
rrcavcav DepthDepth--shiftshiftrrcavcav DepthDepth shiftshift
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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
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Electron ConElectron Con
headhead
variable evariable e--
Dave RogersDave Rogers
ntaminationntamination
1 mm lead1 mm leadheadhead
removes removes variable evariable e--
adds known eadds known e--
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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
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kkQQ for Cylfor Cyl
Dave RogersDave Rogers
indrical Chambersindrical Chambers
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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
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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
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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
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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
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ReferenceReference
Electron
ReferenceReference
Electron
QQ kMPD Qgr
Qw kMPD
kkkk
e Dosimetrye Dosimetry
n Beams
e Dosimetrye Dosimetry
n Beams
CoNk 60 CowDecalR Nk ,50
kkkkQQ
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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
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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
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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
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Electron BElectron BElectron BElectron B
Dave RogersDave Rogers
Beam QualityBeam QualityBeam QualityBeam Quality
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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
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kk´́RR5050 for Cylfor CylRR5050yy
Dave RogersDave Rogers
lindrical Chamberslindrical Chambers
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kk´́RR5050 for for RR5050
Dave RogersDave Rogers
pp Chambers pp Chamberspppp
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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
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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
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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
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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
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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
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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
,
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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
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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
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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
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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 ,
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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
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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,
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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
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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