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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2
RationaleRationale
Radiation dose delivered to the target
and surrounding tissues is one of the
major predictors of radiotherapytreatment outcome (compare part 3 of
the course) !t is generally assumed that
the dose must "e accurately delivered#ithin $%&' of the prescri"ed dose to
ensure the treatment aims are met
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 3
"jectives"jectives
• *o understand the relevance of radiation dose*o understand the relevance of radiation dose
and dosimetry for radiotherapyand dosimetry for radiotherapy
• *o "e a"le to e+plain the difference "et#een*o "e a"le to e+plain the difference "et#een
a"solute and relative dosimetrya"solute and relative dosimetry• *o "e a"le to discuss the features of the most*o "e a"le to discuss the features of the most
common dosimeters in radiotherapy:common dosimeters in radiotherapy:
ioniation cham"ers, semiconductors,ioniation cham"ers, semiconductors,thermoluminescence dosimeters (*-D) andthermoluminescence dosimeters (*-D) and
filmfilm
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .
/ontents of lecture 2/ontents of lecture 2
0 1"solute and relative dosimetry0 1"solute and relative dosimetry
2 *he dosimetric environment: phantoms2 *he dosimetric environment: phantoms
3 Dosimetric techniques3 Dosimetric techniques physical "acgroundphysical "acground
practical realiationpractical realiation
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '
0 1"solute and relative dosimetry0 1"solute and relative dosimetry
Absolute dosimetry is a technique that yieldsinformation directly on a"sor"ed dose in y *his
a"solute dosimetric measurement is also referred to
as cali"ration 1ll further measurements are then
compared to this no#n dose under referenceconditions *his means 4
relative dosimetry is performed !n general no
conversion coefficients or correction factors are
required in relative dosimetry since it is only thecomparison of t#o dosimeter readings, one of them
"eing in reference conditions
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment
1"solute dosimetry 1"solute dosimetry
Required for every radiation qualityRequired for every radiation quality
onceonce
Determination of a"solute dose (in y)Determination of a"solute dose (in y)at one reference point in a phantomat one reference point in a phantom
6ell defined geometry: ;g #ater6ell defined geometry: ;g #ater
phantom, 077cm 89D, 07+07cmphantom, 077cm 89D, 07+07cm22
fieldfieldsie, depth 07cmsie, depth 07cm
8ollo#s protocols (compare part 07)8ollo#s protocols (compare part 07)
O f t re me ndo us
i m po r ta nce:
I f t he a bso l u te dos i me t r y
is i nco r rec t E V E R Y T H I N
G
w i l l be w ro n
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment >
1ns#er 1ns#er FALSE – 1Gy = 1J/kg. Delivering this amount
of energy oul! raise the tem"erature of
tissue #y less than $.$$1o%. Even for a 1$$kg
"erson it is mu&h less than the energy
&onsume! ith a #ol of muesli – "lease note
the amount of energy in foo! is often liste! onthe "a&kage.
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 00
;+amples for relative dosimetry;+amples for relative dosimetry
/haracteriation of a radiation "eam/haracteriation of a radiation "eam percentage depth dose, tissue ma+imumpercentage depth dose, tissue ma+imum
ratios or similar ratios or similar
profilesprofiles
Determination of factors affecting outputDetermination of factors affecting output field sie factors, applicator factorsfield sie factors, applicator factors
filter factors, #edge factorsfilter factors, #edge factors patient specific factors (patient specific factors (e.g.e.g. electron cut&electron cut&
out)out)
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 02
Percentage depth dosePercentage depth dose
measurementmeasurement ?ariation of dose?ariation of dose
in a mediumin a medium
(typically #ater)(typically #ater)#ith depth#ith depth
!ncludes!ncludes
attenuation andattenuation andinverse squareinverse square
la# componentsla# components
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 03
Percentage depth dosePercentage depth dose
Relates dose
at different
depths in water
!or the patient"
to the dose at the
depth of dose
ma#imum $ note
that the y a#is is
relati%e&&&
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 0.
*1R, *@R, *PR*1R, *@R, *PR
Relative dosimetry for isocentric treatmentRelative dosimetry for isocentric treatment
set&up (compare part ')set&up (compare part ')
1ll can "e converted into percentage depth 1ll can "e converted into percentage depth
dosedose *1R A ratio of dose in phantom #ith + cm*1R A ratio of dose in phantom #ith + cm
overlaying tissue to dose at the same point in air overlaying tissue to dose at the same point in air
*@R A ratio of dose #ith + cm overlaying tissue to*@R A ratio of dose #ith + cm overlaying tissue to
dose at dose ma+imum (detector position fi+ed)dose at dose ma+imum (detector position fi+ed)
*PR as *@R "ut as a ratio to dose at a reference*PR as *@R "ut as a ratio to dose at a reference
point (point (e.g.e.g. 07cm overlaying tissue)07cm overlaying tissue)
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 0'
*@R, *PR*@R, *PR
@imics isocentric@imics isocentric
conditionsconditions
*@R is a special*@R is a special
case of *PRcase of *PR
#here the#here the
referencereference
phantom depth isphantom depth isdepth ofdepth of
ma+imum dosema+imum dose
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 0
utput factorsutput factors
/ompare dose #ith dose under/ompare dose #ith dose under
reference conditionsreference conditions
different field siesdifferent field sies #edge factor #edge factor
tray factor tray factor
applicator factor applicator factor electron cutout factor electron cutout factor
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 0B
;+ample: #edge factor ;+ample: #edge factor
+ose under
reference
conditions
,ould also in%ol%e different field si-es and.or
different depths of the detector in the phantom
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 27
1ns#er 1ns#er
Relative dosimetry: #e relate the dose #ith different aluminium
or copper filters in the "eam to the dose
#ithout the filters to determine #hich filterthicness attenuates the "eam to half itsoriginal intensity
the result is independent of the actual dose
given & #e could measure for 07s or 27s or57s each time, as long as #e ensure theirradiation is identical for all measurements
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 20
2 *he dosimetric environment2 *he dosimetric environment
PhantomsPhantoms 1 phantom represents the radiation properties of 1 phantom represents the radiation properties of
the patient and allo#s the introduction of athe patient and allo#s the introduction of a
radiation detector into this environment, a tas thatradiation detector into this environment, a tas that#ould "e difficult in a real patient#ould "e difficult in a real patient
1 very important e+ample is the scanning #ater 1 very important e+ample is the scanning #ater
phantomphantom
1lternatively, the phantom can "e made of sla"s of 1lternatively, the phantom can "e made of sla"s oftissue mimicing material or even shaped as atissue mimicing material or even shaped as a
human "ody (anthropomorphic)human "ody (anthropomorphic)
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 22
9canning #ater9canning #ater
phantomphantom
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2.
*issue equivalent materials*issue equivalent materials
@any specifically manufactured materials@any specifically manufactured materials
such as solid #ater (previous slide), #hitesuch as solid #ater (previous slide), #hite
#ater, plastic #ater, 4#ater, plastic #ater, 4 Polystyrene (good for megavoltage "eams,Polystyrene (good for megavoltage "eams,
not ideal for lo# energy photons)not ideal for lo# energy photons)
Perspe+ (other names: P@@1, Ple+iglas) &Perspe+ (other names: P@@1, Ple+iglas) &
tissue equivalent composition, "ut #ith highertissue equivalent composition, "ut #ith higherphysical density & correction is necessaryphysical density & correction is necessary
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2'
1nthropomorphic phantom 1nthropomorphic phantom
)hole body
phantom: /RT
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 25
1llo#s placement of radiation detectors in 1llo#s placement of radiation detectors in
the phantom (sho#n here are *-Ds)the phantom (sho#n here are *-Ds)
Includes
inhomoeneities
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2
R1EDR1ED
phantomphantom
torso
,T slice
throuh lun
Head with
T(+ holes
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2B
Pediatric phantomPediatric phantom
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2>
9ome remars on phantoms9ome remars on phantoms
!t is essential that they are tested prior to use!t is essential that they are tested prior to use physical measurements & #eight, dimensionsphysical measurements & #eight, dimensions
radiation measurements & /* scan, attenuationradiation measurements & /* scan, attenuation
checschecs
/heaper alternatives can also "e used/heaper alternatives can also "e used #a+ for shaping of humanoid phantoms#a+ for shaping of humanoid phantoms
cor as lung equivalentcor as lung equivalent
1s long as their properties and limitations are 1s long as their properties and limitations areno#n & they are usefulno#n & they are useful
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 30
Principles of radiation detectionPrinciples of radiation detection
!oniation cham"er !oniation cham"er
eiger @ueller /ounter eiger @ueller /ounter *hermoluminescence dosimetry*hermoluminescence dosimetry
8ilm8ilm
9emiconductors9emiconductors
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 32
Detection of !oniation in 1ir Detection of !oniation in 1ir
/dapted
from ,ollins
4556
Ion chamber
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 33
Detection of !oniation in 1ir Detection of !oniation in 1ir
/dapted
from
2etcalfe
6778
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 35
/ross section through a 8armer type/ross section through a 8armer type
cham"er (from @etcalfe 0>>5)cham"er (from @etcalfe 0>>5)
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 3
!oniation /ham"ers!oniation /ham"ers
8armer 75 cc8armer 75 cc
cham"er andcham"er and
electrometer electrometer
@ost important@ost important
cham"er incham"er in
radiotherapyradiotherapy
dosimetrydosimetry
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 3B
;lectrometer ;lectrometer
1rom the chamber
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 3>
!oniation cham"ers!oniation cham"ers
Relatively large volume for small signalRelatively large volume for small signal
(0y produces appro+imately 35n/ in(0y produces appro+imately 35n/ in
0cc of air)0cc of air) *o improve spatial resolution at least in*o improve spatial resolution at least in
one dimension parallel plate typeone dimension parallel plate type
cham"ers are usedcham"ers are used
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .7
Parallel plate cham"ersParallel plate cham"ers
1rom 2etcalfe et al 6779
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .2
Parallel Plate !oniationParallel Plate !oniation
/ham"ers & e+amples/ham"ers & e+amples @arus cham"er @arus cham"er
smallsmall
designed fordesigned forelectronselectrons
Colt cham"er Colt cham"er
ro"ustro"ust
em"edded inem"edded inpolystyrene sla"polystyrene sla"
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .3
6ell type ioniation cham"er 6ell type ioniation cham"er
8or cali"ration of8or cali"ration of
"rachytherapy"rachytherapy
sourcessources
3rachytherapy
source
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment ..
!oniation cham"er type survey!oniation cham"er type survey
metersmeters not as sensitive as &@ devices "ut not affected "ynot as sensitive as &@ devices "ut not affected "y
pulsed "eams such as occur #ith acceleratorspulsed "eams such as occur #ith accelerators
"ecause of the a"ove,"ecause of the a"ove,
this is the preferredthis is the preferred
device around highdevice around highenergy radiotherapyenergy radiotherapy
acceleratorsaccelerators
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .'
eiger&@ueller /ounter eiger&@ueller /ounter
Eot a dosimeter & just aEot a dosimeter & just a
counter of radiation eventscounter of radiation events
?ery sensitive?ery sensitive -ight #eight and-ight #eight and
convenient to useconvenient to use
9uita"le for miniaturiation9uita"le for miniaturiation
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .5
eiger&@ueller (&@) Deviceseiger&@ueller (&@) Devices
Gseful forGseful for area monitoringarea monitoring
room monitoringroom monitoring
personnelpersonnel monitoringmonitoring
/are required in regions of high dose rate/are required in regions of high dose rate
or pulsed "eams as reading may "eor pulsed "eams as reading may "e
inaccurateinaccurate
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .
*hermoluminescence*hermoluminescence
dosimetry (*-D)dosimetry (*-D) 9mall crystals9mall crystals
@any different materials@any different materials
Passive dosimeter & no ca"les requiredPassive dosimeter & no ca"les required
6ide dosimetric range (6ide dosimetric range (µµy to 077s ofy to 077s of
y)y)
@any different applications@any different applications
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .B
?arious *-D types?arious *-D types
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment .>
9implified scheme of the *-D9implified scheme of the *-D
processprocess
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '7
*-D glo# curves*-D glo# curves
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '0
lo# curveslo# curves
1llo# research 1llo# research
1re po#erful
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '2
*he role of different dopants*he role of different dopants
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '3
Importance o thermalImportance o thermal
treatmenttreatment Determines the arrangement ofDetermines the arrangement of
impuritiesimpurities
sensitivitysensitivity fadingfading
response to different radiation qualitiesresponse to different radiation qualities
@aintain thermal treatment constant@aintain thermal treatment constant
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '.
DoseDose
response ofresponse of-i8:@g,*i:-i8:@g,*i:
#ide dosimetric#ide dosimetricrangerange
#atch#atchsupralinearitysupralinearity
f
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment ''
?ariation of *-D response #ith?ariation of *-D response #ith
radiation qualityradiation quality
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '5
@aterials: oh #hat a choice@aterials: oh #hat a choice
-i8:@g,*i (the JgoldJ standard)-i8:@g,*i (the JgoldJ standard)
/a8/a822 (all natural, or #ith @n, Dy or *m)(all natural, or #ith @n, Dy or *m)
/a9/a9..
KeKe
1l 1l2233 :/ (record sensitivity:/ (record sensitivity ≤≤ 0uy)0uy)
-i8:@g,/u,P (the ne# star=)-i8:@g,/u,P (the ne# star=)
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '
*-D reader *-D reader
photomultiplier "asedphotomultiplier "ased planchet and hot Eplanchet and hot E22 gas heatinggas heating
availa"leavaila"le
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 'B
!hat can one e"pect###!hat can one e"pect###
Reproduci"ility: single chipReproduci"ility: single chip ±± 2 (70y,2 (70y,09D)09D)
1ccuracy (. chips standard, 2 chips 1ccuracy (. chips standard, 2 chips
measurement)measurement) ±± 3 (70y, >'3 (70y, >'confidence)confidence)
a"out 37 minutes per measurementa"out 37 minutes per measurement
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment '>
Radiographic filmRadiographic film
Reduction of silver halide to silver Reduction of silver halide to silver
Requires processing &&&F pro"lems #ithRequires processing &&&F pro"lems #ith
reproduci"ilityreproduci"ility *#o dimensional dosimeter *#o dimensional dosimeter
Cigh spatial resolutionCigh spatial resolution
Cigh atomic num"er &&&F variations ofCigh atomic num"er &&&F variations ofresponse #ith radiation qualityresponse #ith radiation quality
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 57
Radiographic filmRadiographic film
,ross section
Often prepac*edfor ease of use
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 50
8ilm: dose response8ilm: dose response
;valuation of film via;valuation of film via
optical densityoptical density
D A log (!D A log (!77 % !)% !) Densitometers areDensitometers are
commerciallycommercially
availa"leavaila"le
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 52
Radiographic film dosimetry inRadiographic film dosimetry in
practicepractice Depends on e+cellentDepends on e+cellent
processor
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 5.
9emiconductor Devices9emiconductor Devices
DiodesDiodes
@98;* detectors@98;* detectors
+iodes for water phantom
measurements
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 5'
DiodesDiodes
1rom 2etcalfe et al. 6779
2ostly used li*ea photocell eneratin
a %oltae proportional
to the dose recei%ed
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 55
@etal +ide 9emiconductor @etal +ide 9emiconductor
8ield ;ffect *ransistor 8ield ;ffect *ransistor
1rom 2etcalfe et al. 6779
2O'1ETs ; e#tremely
small sensiti%e %olume
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 5
0 irradiation
2 /harge
carriers trapped
in 9i su"strate
3 /urrent"et#een source
and drain altered
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 5>
Diodes and other 9olid 9tateDiodes and other 9olid 9tate
DevicesDevices 1dvantages 1dvantages
direct readingdirect reading
sensitivesensitive
small siesmall sie
#aterproofing#aterproofing
possi"lepossi"le
DisadvantagesDisadvantages temperaturetemperature
sensitivesensitive
sensitivity maysensitivity may
change &&F re&change &&F re&
cali"ration necessarycali"ration necessary
regular
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 7
9ummary of lecture 29ummary of lecture 2
Ion chambers 'emiconductors T(+s 1ilm
/d%antaes )ell understood<
accurate< %ariety of
forms a%ailable
'mall< robust 'mall< no cables
re0uired
Two dimensional<
ease of use
+isad%antaes (are< hih %oltae
re0uired
Temperature
dependence
+elayed readout<
comple# handlin
Not tissue
e0ui%alent< not
%ery reproducible
,ommon use Reference
dosimetry< beam
scannin
3eam scannin< in
%i%o dosimetry
+ose %erification<
in %i%o dosimetry
=/< assessment of
dose distributions
,omment 2ost common and
important
dosimetric
techni0ue
New de%elopments
!2O'1ETs" may
increase utility
/lso used for
dosimetric
intercomparisons
!audits"
New de%elopments
!radiochromic
film" may increase
utility
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 0
eneral 9ummary: Physicseneral 9ummary: Physics !n radiotherapy,!n radiotherapy, photonsphotons ( Rays and gamma rays)( Rays and gamma rays)
andand electronselectrons are the most important radiation typesare the most important radiation types 1ccuracy of dose delivery is essential for good 1ccuracy of dose delivery is essential for good
practice in radiotherapypractice in radiotherapy
1"solute dosimetry 1"solute dosimetry determines the a"sor"ed dose indetermines the a"sor"ed dose in
ray at a #ell&defined reference pointray at a #ell&defined reference point RelativeRelativedosimetrydosimetry relates then the dose in all other points orrelates then the dose in all other points orthe dose under different irradiation conditions to thisthe dose under different irradiation conditions to thisa"solute measurementa"solute measurement
*here are*here are many different techniquesmany different techniques availa"le foravaila"le fordosimetry & none is perfect and it requires training anddosimetry & none is perfect and it requires training ande+perience to choose the most appropriate techniquee+perience to choose the most appropriate techniquefor a particular purpose and interpret the resultsfor a particular purpose and interpret the results
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Radiation Protection in Radiotherapy Part 2, lecture 2: Dosimetry and equipment 2
6here to et @ore6here to et @ore
!nformation!nformation @edical physicists@edical physicists
*e+t"oos:*e+t"oos:
Ihan 8 *he physics of radiation therapy 0>>. @etcalfe PL Iron *L Co"an P *he physics of
radiotherapy &rays from linear accelerators 0>>
/em"er C !ntroduction to health physics 0>B3
6illiams ML *h#aites D Radiotherapy Physics 0>>3
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1ny questions= 1ny questions=
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Question:Question:
6hich radiation detectors could "e useful6hich radiation detectors could "e useful
for in vivo dosimetry and #hy=for in vivo dosimetry and #hy=
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