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11
IRRADIATORSIRRADIATORS
Terry Terry YoshizumiYoshizumi, PhD, PhD
September 11, 2006September 11, 20068:00 am8:00 am--5:00 pm5:00
pm
Hock Plaza AuditoriumHock Plaza AuditoriumDuke University
Medical Center, Erwin RoadDuke University Medical Center, Erwin
Road
Radiation Countermeasures Center of Research Excellence
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22
AcknowledgementsAcknowledgements
Sam Brady Sam Brady Garrett Garrett MuramotoMuramotoJohn
ChuteJohn ChuteGiaoGiao NguyenNguyenGreta Greta
TonchevaTonchevaLauren DaigleLauren DaigleDave JorgensenDave
Jorgensen
Greg EganGreg EganNetitiNetiti MooriMooriBrad ThrasherBrad
ThrasherBeverly Beverly
SteffeySteffeyOanaOanaCraciunescuCraciunescu
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77
XX--ray irradiatorray irradiator
•• Production of xProduction of x--rays rays
((bremsstrahlungbremsstrahlung))
•• How the xHow the x--ray machine worksray machine works••
BremsstrahlungBremsstrahlung XX--ray spectrumray spectrum•• Factors
affecting Factors affecting dosimetrydosimetry•• Case study (John
Chute)Case study (John Chute)
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Production of xProduction of x--rays (rays
(bremsstrahlungbremsstrahlung))
Charged particle (e.g., electron) passing near a nucleus Charged
particle (e.g., electron) passing near a nucleus may be deflected
by the strong electrical forces exerted may be deflected by the
strong electrical forces exerted on it by the nucleus on it by the
nucleus As the projectile electron passes by the nucleus, it slows
As the projectile electron passes by the nucleus, it slows down,
changes its course, and leaves with reduced down, changes its
course, and leaves with reduced kinetic energy. This loss in
kinetic energy reappears as kinetic energy. This loss in kinetic
energy reappears as an xan x--ray (called ray (called
bremsstrahlungbremsstrahlung xx--rays)rays)
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99
How the xHow the x--ray machine worksray machine works
AGFA X-RAD 320
X-ray tube
Removable filter
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1010
ANATOMY OF ANODE TUBEANATOMY OF ANODE TUBE
Z=74, High melting point 3380 deg C
Melting point 1083 deg C
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1111
TUBE VOLTAGE AND TUBE CURRENTTUBE VOLTAGE AND TUBE CURRENT
Tube voltage (kVp) Tube current
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1212
CATHODE ASSEMBLYCATHODE ASSEMBLY
Small filament for Small filament for highhigh--resolution
resolution imagingimagingLarger filament Larger filament for higher
for higher intensities (large intensities (large mAmA))
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TARGET ANGLE AND DIRECTION OF TARGET ANGLE AND DIRECTION OF
BREMSSTRAHLUNGBREMSSTRAHLUNG
Target angle 10Target angle 10--20 20 degreesdegreesDirection of
Direction of bremsstrahlungbremsstrahlung radiations radiations
(approx. perpendicular to (approx. perpendicular to the direction
of electrons)the direction of electrons)
See next slideSee next slide
Target angle
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1414
RELATIVE INTENSITY OF RELATIVE INTENSITY OF
BREMSSTRAHLUNGBREMSSTRAHLUNG
For low energy For low energy electrons, radiated electrons,
radiated predominantly at right predominantly at right angle to the
motion of angle to the motion of the particlesthe particlesThe
probability of The probability of
bremsstrahlungbremsstrahlungproduction varies with Zproduction
varies with Z2 2 of the absorbing of the absorbing
materialsmaterials
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1515
BremsstrahlungBremsstrahlung xx--ray spectrumray spectrum
Max. kVp
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1616
FILTERS, AND BEAM RESTRICTORSFILTERS, AND BEAM RESTRICTORS
# 1 # 4 # 8
# types of filters
#1: 1.65 mm Aluminum#4: 0.1 mm Cu + 2.5 mm Al#8: 0.8 mm Tin +
0.25 mm Cu +1.5 mm Al
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Key factors affecting Key factors affecting
dosimetrydosimetry
XX--ray energy (ray energy (kVpkVp))Tube current (Tube current
(mAmA –– milliamperesmilliamperes))Beam filtration (filters)Beam
filtration (filters)DistanceDistanceAttenuation in mouseAttenuation
in mouseBackscatter as a function of field sizeBackscatter as a
function of field size
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Factors affecting Factors affecting dosimetrydosimetry
XX--ray energy (ray energy (kVpkVp) ) ––Rule of Thumb (dose
increases to kVpRule of Thumb (dose increases to kVp22))
22 2
1 1
222 1
1
Dose kVp ( )Dose kVp
kVpDose Dose ( )kVp
•
∼
∼
Example: 120 kVp to 140 kVp
Dose140 kVp ~Dose120kVp * (140/120)2 = 1.36* Dose120kVp
i.e., Dose increases by 36%.
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1919
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Factors affecting Factors affecting dosimetrydosimetry
Tube current (Tube current (mAmA ––
milliamperesmilliamperes))
A change in A change in mAmA results in a results in a directly
proportional change in directly proportional change in the
amplitude of the xthe amplitude of the x--ray ray emission spectrum
at all emission spectrum at all energies.energies.Example: if you
double the Example: if you double the mAmAfrom 200from 200--mA to
400mA to 400--mA, the mA, the area under the curve (xarea under the
curve (x--ray ray quantity) doubles.quantity) doubles.
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Factors affecting Factors affecting dosimetrydosimetry
Effects of beam filtration (filters)Effects of beam filtration
(filters)
Available filtersAvailable filters#1: 1.65 mm Aluminum#4: 0.1 mm
Cu + 2.5 mm Al
#8: 0.8 mm Tin + 0.25 mm Cu +1.5 mm Al
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2222
Factors affecting Factors affecting dosimetrydosimetry
Effects of beam filtration (filters)Effects of beam filtration
(filters)The overall result of added filtration is an increase in
the The overall result of added filtration is an increase in the
effective energyeffective energy of the xof the x--ray beam with an
ray beam with an accompanying accompanying reductionreduction in
xin x--ray quantity.ray quantity.
Peak energy shift
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2323
#4 filter being used in Sands Building
#1 filter #8 filter
#4 filter
#1: 1.65 mm Aluminum#4: 0.1 mm Cu + 2.5 mm Al#8: 0.8 mm Tin +
0.25 mm Cu +1.5 mm Al
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Factors affecting Factors affecting dosimetrydosimetry
Effect of distanceEffect of distance
(source(source--toto--surface distance, SSD, or surface distance,
SSD, or target (focal spot)target (focal spot)--to surface
distance, TSD)to surface distance, TSD)InverseInverse--square law
(dose decreases inversely to the square law (dose decreases
inversely to the square of the distance)square of the
distance)Example: 4Gy *(50cm/100cm)Example: 4Gy *(50cm/100cm)22 =
4Gy*(1/4)=1 = 4Gy*(1/4)=1 GyGy
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XX--ray geometryray geometry-- mousemouse
Dose depends on the source-to-mouse (target) distance. The
closer to the tube, the higher the dose.
Hummm…I feel more heat!
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Factors affecting Factors affecting dosimetrydosimetry
Attenuation in mouseAttenuation in mouseFor 135 For 135 kVpkVp
expect some attenuation in the mouseexpect some attenuation in the
mouse
Backscatter as a function of field sizeBackscatter as a function
of field size
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2727
CASE STUDYCASE STUDY
John Chute, PIJohn Chute, PIObjectivesObjectives
Compare absorbed dose Compare absorbed dose between clinical
protocol and between clinical protocol and direct TLD methoddirect
TLD methodClinical protocol used by Clinical protocol used by
GarretteGarrette: Parameters: : Parameters: 135kVP, 22mA, @ 135kVP,
22mA, @ 100cGy/min, FS (collimated 100cGy/min, FS (collimated
beam): 20 cm x 20 cmbeam): 20 cm x 20 cm
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Mouse Anatomy % Bone MarrowMouse Anatomy % Bone Marrow
Skull:17.6%
Mandible:2.0%
Humerus:2.4%
Forearm:0.7%
Sternum:3.8%
All Ribs:5.0%
Clavicle and Scapula: 1.0%
Spine: 33.7%
Cervical: 4.2%
Thoracic: 7%
Lumbar: 9.9%
Sacral:8.1%
Coccygeal: 2.3%
Pelvis:11.9%
Femur: 5.8%
Tibia: 3.0%
•Mus musculus (Common species of Lab mouse):
-Avg overall length: 16.9cm (head to tail)
-body length: 6-10cm (head to base of tail)
-hind foot: 1.8cm
-Avg weight adult mouse: 17-25g
-Average height: 3-5cm
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TISSUETISSUE--EQUIVALENT MOUSE PHANTOMEQUIVALENT MOUSE
PHANTOM
3.8cm
2.0cm
3.8cm
2.7cm
2.4cm
TLD 11, 12TLD 13, 14TLD 15, 16
12 cm
3 cm0.6 cm0.3 cm1 cm
TLD chips (3 mm x 3 mm x 1 mm thick)
A B C
A B C
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Results: xResults: x--ray irradiatorray irradiator
--13%13%441.36 441.36 ++ 6.12 6.12 cGycGy500 500 cGycGyC C 0.6
cm deep0.6 cm deep
--17%17%427.07 427.07 ++ 37.23 37.23 cGycGy500 500 cGycGyB
(Middle)B (Middle)0.3 cm deep0.3 cm deep
--23%23%406.79 406.79 ++ 15.61 15.61 cGycGy500 500 cGycGyA
(Head)A (Head)1 cm deep1 cm deep
% DIFF% DIFFTLD MEASURED TLD MEASURED DOSEDOSE
CLINICAL CLINICAL SETTINGSETTING100 100 cGycGy/min/min
LOCATIONLOCATION
Dose rate suspicious
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Clinical Setting 500 Clinical Setting 500 cGycGy
X-ray Mouse Dose (cGy)
406.79 427.07 441.36
0.00
100.00
200.00
300.00
400.00
500.00
A (1.0 cm) B (0.3 cm) C (0.6 cm)
TLD locations
Dos
e (c
Gy)
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3232
New Calibration factors New Calibration factors for Garrett
geometryfor Garrett geometry
2.72.785.085.0AVERAGEAVERAGE
1.21.288.388.3CC
7.47.485.485.4BB
3.13.181.181.1AA
SD Dose RateSD Dose Rate((cGycGy/min)/min)
Dose Rate Dose Rate ((cGycGy/min)/min)
LocationLocation
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Why mice did not die?Why mice did not die?
--18%18%595.1 +/595.1 +/-- 19.119.170070077
% Diff% DiffNew DR New DR (85.0 +/(85.0 +/-- 2.7 2.7
cGycGy/min)/min)
Clinical DRClinical DRused used
(100 (100 cGycGy/min)/min)
Time (min)Time (min)
Target 700 cGy was actually 595 +/- 19 cGy.
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3434
STD=50 CM
Dose Rate (DR) in cGy/min
d cm
2
2
50 cm cGyDesired Dose (cGy)=( ) x DR ( ) x T(min)d cm min
Desired Dose (cGy)T(min) = 50 cm cGy( ) x DR ( )d cm min
A
B
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GEOMETRY GEOMETRY
STD=45.5 cmSTD=45.5 cm3.5 cm
STD=50 cm
2 cm
46.5 cm
A: STD=45.5 cm
3 cm
0.5 cm deep
4.8 cm
B: 44.2 cm
1 cm below
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Results of mice Results of mice dosimetrydosimetryxx--ray
irradiatorray irradiator
500 500 cGycGy504 504 cGycGy475.18 475.18 cGycGyDose for 5 min
Dose for 5 min exposureexposure
100 100 cGycGy/min/min100.7 100.7 cGycGy/min/min95.0 95.0
cGycGy/min/minDose rateDose rate
Dose rate being Dose rate being used clinically by used
clinically by Chute groupChute group
B:B:Assume sourceAssume source--toto--target distance target
distance =44.2 cm=44.2 cm
A:A:Assume sourceAssume source--toto--Target distance Target
distance =45.5 cm=45.5 cm
LOCATIONLOCATION
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DiscussionsDiscussions
Sources of inaccuraciesSources of inaccuraciesLookLook--up table
(BSF)up table (BSF)-- probably minorprobably minorGeometry changed
since Geometry changed since originakloriginaklcalibration
(major)calibration (major)Scatter geometry different in mice in the
Scatter geometry different in mice in the plastic holder (not
uniform water phantom)plastic holder (not uniform water
phantom)
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Gamma ray irradiatorGamma ray irradiatorJL ShepherdJL
ShepherdMark IMark I
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Gamma ray irradiatorGamma ray irradiator
Decay scheme (CsDecay scheme (Cs--137)137)Key differences from
XKey differences from X--rayrayCase studyCase studyQuality
assurance noteQuality assurance note
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Decay scheme (CsDecay scheme (Cs--137)137)
HalfHalf--life= 30 yrslife= 30 yrsEmits Emits ββ−−11 particles
particles (electrons)(electrons)Gamma at 662 Gamma at 662
keVkeV
137 137 055 56 -1Cs Ba + + +β ν γ→
+ -
137 137 055 56 -1
n p + e + + energy
Cs Ba + + ν +
γ
β γ
→
→
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Key differences from XKey differences from X--ray irradiatorray
irradiator
Energy: CsEnergy: Cs--137 662 137 662 keVkeVXX--ray 135 ray 135
kVpkVp ((aveave. energy ~45 . energy ~45 keVkeV))
(average energy ~135 * 1/3= 45 (average energy ~135 * 1/3= 45
keVkeV))Need for annual decay correction for CsNeed for annual
decay correction for Cs--137137
The dose rates must be decreased 2.3% per year.The dose rates
must be decreased 2.3% per year.
0.693 1-λ*t - 30e = e 0.977
yryr•
=
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CsCs--137 Irradiator Dimension137 Irradiator Dimension
Turntable30 cm diam.
37 cm high
Cs-137 source will be raised
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CsCs--137 Irradiator (Chute)137 Irradiator (Chute)
rotating table
3”=7.6 cm
4.8 cm
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Factors affecting Factors affecting dosimetrydosimetry
NonNon--uniform irradiation of mice due to uniform irradiation
of mice due to rotating tablerotating tableDose rate point taken at
central point and Dose rate point taken at central point and assume
same dose distribution (not true)assume same dose distribution (not
true)
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CASE STUDYCASE STUDY
John Chute, PIJohn Chute, PIObjectivesObjectives
Compare absorbed dose Compare absorbed dose between clinical
protocol and between clinical protocol and direct TLD methoddirect
TLD methodExposure T=0.76 minExposure T=0.76 minTarget dose =500
Target dose =500 cGycGy
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Geometry issues need to Geometry issues need to be addressedbe
addressed Beam angle and TLD chip–angle dependency
The beam not always perpendicular to the chips
TLD chipsΘ
Cs-137 source
Goals: •Understand angle dependency•Minimize angle effects in
dosimetry
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4747
8/15/2006 TLD runs:Cs8/15/2006 TLD runs:Cs--137 geometry137
geometry
#1
#2
#3
TLD perpendicular,middle
#1
#2 TLD parallel to beam, middle
TLD parallel to beam, top, same as x-ray
#3
rotation
TLD chip 3 x 3 x 1 mm
Beam direction
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4848
A B C
CLINICAL PROTOCOL DOSE SET TO 500 cGySet-up #1
Gold Standard (TLD Cs-137)
448.39 430.45474.52 451.12
0.00
100.00
200.00
300.00
400.00
500.00
600.00
A B C average
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4949
Geometry #2, target dose =500 Geometry #2, target dose =500
cGycGy
#2 TLD parallel to beam, middle
Case #2
443.52496.59
457.95 466.02
0.00
100.00
200.00
300.00
400.00
500.00
600.00
A B C average
dose
(cG
y)
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5050
Case #3: xCase #3: x--ray geometry, Target 500 ray geometry,
Target 500 cGycGy
TLD parallel to beam, top, same as x-ray
#3
3.8cm
2.0cm
3.8cm
2.7cm
2.4cm
TLD 11, 12TLD 13, 14TLD 15, 16
12 cm
3 cm0.6 cm0.3 cm1 cm
A B C
Case #3: x-ray geometry
465.32
429.90
474.10456.44
360.00380.00
400.00420.00440.00460.00
480.00500.00
A B C average
Dos
e (c
Gy)
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5151
New calibration factors for Garrett geometryNew calibration
factors for Garrett geometry
10.610.6600.6600.6#3 (spine curve)#3 (spine curve)
12.612.6613.2613.2#2 (middle)#2 (middle)
12.812.8593.6593.6#1 (middle, gold #1 (middle, gold
standard)standard)
SD (SD (cGycGy/min)/min)DR (DR
(cGycGy/min)/min)geometrygeometry
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Irradiator Irradiator DosimetyDosimety Quality Assurance
NoteQuality Assurance Note
Whenever setWhenever set--up changes, consult your up changes,
consult your physicists (physicists (OanaOana and Beverly, and
Beverly, RadRad OncOnc or or RadccoreRadccore HP group) HP group)
Geometry specific Geometry specific directdirect measurements would
measurements would improve confidence and accuracyimprove
confidence and accuracyCalibration factors for specific geometries
may Calibration factors for specific geometries may be posted be
posted in the webin the web--sitesiteDose validation is important
across the Dose validation is important across the RadccoreRadccore
affiliatesaffiliates
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5454
Irradiator safety issuesIrradiator safety issues
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5555
Irradiator safety issuesIrradiator safety issues
DonDon’’t lose your fingerst lose your fingersUnderstand
radiation levels in normal Understand radiation levels in normal
operationsoperations
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Radiation level under normal operationsRadiation level under
normal operations
X-ray beam on
Cs-137Source off
8 µR/hr @ 1’
9 µR/hr @ 2 ‘
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R R 1 hrDose equivalent ( Rem ) = 8 * *10 min * = 1.3 x 10 R (or
Rem) hr 10 µR 60 minµ
Assume 10 min exposure @ 1 ft, then
Recall WB limit = 5 Rem per yr No radiation risks!
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5757
CsCs--137 source up137 source up
130D
300C
80B
130A
waist level 3-ft high (1 ft away from
wall) uR/hr
location
A
B
C
D
A
At A, 5 x 10-5 Rem for 10 min exposure(Annual limit = 5 Rem)
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5858
Safety SummarySafety Summary
Watch your fingers!Watch your fingers!Under normal operating
conditions, no Under normal operating conditions, no radiation
risks exist.radiation risks exist.