IRRADIATORS · 2017. 10. 2. · IRRADIATORS Terry Yoshizumi, PhD September 11, 2006 8:00 am-5:00 pm Hock Plaza Auditorium Duke University Medical Center, Erwin Road Radiation Countermeasures

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

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

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)

88

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)

99

How the xHow the x--ray machine worksray machine works

AGFA X-RAD 320

X-ray tube

Removable filter

1010

ANATOMY OF ANODE TUBEANATOMY OF ANODE TUBE

Z=74, High melting point 3380 deg C

Melting point 1083 deg C

1111

TUBE VOLTAGE AND TUBE CURRENTTUBE VOLTAGE AND TUBE CURRENT

Tube voltage (kVp) Tube current

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))

1313

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

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

1515

BremsstrahlungBremsstrahlung xx--ray spectrumray spectrum

Max. kVp

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

1717

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

1818

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%.

2020


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.

2121


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

2222


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

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

2424


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

2525

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!

2626


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

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

2828

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

2929

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

3030

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

3131

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)

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

3333

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.

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

3535

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

3636

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

3737

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)

3838

Gamma ray irradiatorGamma ray irradiatorJL ShepherdJL ShepherdMark IMark I

3939

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

4040

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

→

→

4141

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•

=

4242

CsCs--137 Irradiator Dimension137 Irradiator Dimension

Turntable30 cm diam.

37 cm high

Cs-137 source will be raised

4343

CsCs--137 Irradiator (Chute)137 Irradiator (Chute)

rotating table

3”=7.6 cm

4.8 cm

4444


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)

4545

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

4646

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

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

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

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)

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)

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

5252

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

5454

Irradiator safety issuesIrradiator safety issues

5555

Irradiator safety issuesIrradiator safety issues

DonDon’’t lose your fingerst lose your fingersUnderstand radiation levels in normal Understand radiation levels in normal operationsoperations

5656

Radiation level under normal operationsRadiation level under normal operations

X-ray beam on

Cs-137Source off

8 µR/hr @ 1’

9 µR/hr @ 2 ‘

-66

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!

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)

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.

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IRRADIATORS · 2017. 10. 2. · IRRADIATORS Terry Yoshizumi, PhD September 11, 2006 8:00 am-5:00 pm Hock Plaza Auditorium Duke University Medical Center, Erwin Road Radiation Countermeasures