Ionizing Radiation Group K.B. Lee · 2013-10-15 · 22 May 20, 2005 K. B. Lee (Ionizing Radiation...
Transcript of Ionizing Radiation Group K.B. Lee · 2013-10-15 · 22 May 20, 2005 K. B. Lee (Ionizing Radiation...
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11Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Ionizing Radiation GroupK.B. Lee [email protected]
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22Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Contents
hA standard equipment for metrology in nuclear medicine
hWhy Monte Carlo technique in nuclear medicine
hPENELOPE Monte Carlo program
hMonte Carlo modeling
hPreliminary simulation results
hFuture plan
hA standard equipment for metrology in nuclear medicine
hWhy Monte Carlo technique in nuclear medicine
hPENELOPE Monte Carlo program
hMonte Carlo modeling
hPreliminary simulation results
hFuture plan
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33Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Traveling standard
Radionuclide calibrator : The de facto standard instrument for activity measurement of radiopharmaceuticals in the medical institutes
A new ion chamber has been developed in KRISS, serving as a traveling standard used to calibrate the radionuclide calibrators in hospitals and clinics.
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44Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Ionization chamber
hWell-type, re-entrant
hGamma sensitive
hWell diameter : 2 inches
hCENTRONICS
h15 atm Argon gas
hWell-type, re-entrant
hGamma sensitive
hWell diameter : 2 inches
hCENTRONICS
h15 atm Argon gas
hWell liner
hsample holders of different heights
hKeithley 6517A electrometer
hCurrent mode
hBuilt-in power supply
hWell liner
hsample holders of different heights
hKeithley 6517A electrometer
hCurrent mode
hBuilt-in power supply
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55Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
IC characterization
Efficiency variation over applied voltage
Efficiency variation over source position
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66Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Consistency check
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77Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Scheme of QA in radioassay
hCalibration service (KRISS)hCalibration service (KRISS)
hIntercomparison and proficiency test (KFDA)hIntercomparison and proficiency test (KFDA)
Accuracy requirements• Diagnostic accuracy
total : < 10 %instrumental : < 5 %
• Therapeutic accuracytotal : < 5 %instrumental : < 2 %
Accuracy requirements• Diagnostic accuracy
total : < 10 %instrumental : < 5 %
• Therapeutic accuracytotal : < 5 %instrumental : < 2 %
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88Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Calibration factor
calibration factor
( pA => MBq )
hSolution volume and density hGlass wall thickness of container
( vial and syringe)hMetal wall thickness of chamber
hSolution volume and density hGlass wall thickness of container
( vial and syringe)hMetal wall thickness of chamber
• The chamber needs to be calibrated to obtain the activity from the current measured.
• Calibration factor depends on the measurement geometry
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99Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Why Monte Carlo technique
Solution volume
0.5 ml, 1 ml, 2ml, 2.5 ml, 5ml
Solution volume
0.5 ml, 1 ml, 2ml, 2.5 ml, 5ml+
• The chamber calibration factor depends on the volume of the source and on the type of the measurement vessel.
• Modification of the geometry requires to recalibrate the chamber in the new geometry.
• Experimental determination of all the calibration factors cost much time and money
• Use the PENELOPE Monte Carlo code to calculate the calibration factor under varying conditions and complement the experimental determinations.
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1010Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
• PENetration and Energy LOss of Positrons and Electrons
• PENELOPE V 2003• Applicable from 100 eV to 1 GeV energy• Photon, electron and positron simulation
– Photon : Rayleigh, photoelectric, compton, pair production
– Electron/positron : elastic, inelastic, Bremsstrahlung, positron annihilation
• Neither hadronic interactions nor braggdiffraction
• Atomic relaxation (characteristic X-ray, Auger electron)
PENELOPE code
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1111Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
• Composed of 35 elementary volumes described by 62 surfaces– Radioactive solution in the glass vial– PMMA liner and source holder– Ionization chamber
• The materials – Water, air, aluminum, iron, argon, pyrex glass, rubber,
stainless steel • Established using the specifications of the
manufacturer for the pressure, the type of materials, and the dimension of the chamber
Simulated model
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1212Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Simulation parameters
• Eabs : cut-off energy for absorption• Wcc, Wcr : cut-off energy loss for hard interactions• C1 : determine the mean free path between hard elastic events • C2 : maximum average fractional energy loss in a single step
Eabs (electron)(keV)
Eabs (photon)(keV)
Eabs (positron)(keV)
C1, C2 Wcc, Wrc
(keV)
Argon 0.1 0.1 0.1 0.05 0.5
1The other materials
10 1 10 0.1
• Best compromise between speed and accuracy • Each calculation begins with different random generator seeds
to avoid any correlation in the simulation. • No variance reduction method
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1313Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Geometry
8R vial geometry (in cm)IC geometry (in mm)
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1414Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
IC and vial simulated
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1515Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Simulation result (I)
Deposited energy distribution in the gas for 100 keVphotons generated inside the source volume
Source volume Deposited energy difference
0.5 ml (971.7 ± 1.5) eV 2.8 %
1 ml (947.4 ± 1.5) eV 0.3 %
1.5 ml (945.0 ± 1.5) eV 0.0 %
2 ml (941.3 ± 1.5) eV -0.4 %
2.5 ml (929.9 ± 1.5) eV -1.6 %
Source volume dependence
Response depends on volume of solution(different volume => different
geometry and attenuation)
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1616Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Simulation result (II)
Vial type Wall thickness
Deposited energy Difference
8R vial 1 mm
10R vial 1 mm (961.5 ± 1.5) eV -1.0 %
1.2 mm
(971.7 ± 1.5) eV 0.0 %
P6 vial (877.4 ± 1.5) eV -9.1 %
Vial type dependence
• Variation in wall thickness of glass vials is ± 0.05 mm in 1 mm
• Different wall thickness requires to use different calibration factors
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1717Impact of IT in AIST, Japan May 20, 2005 K. B. Lee (Ionizing Radiation Group)K. B. Lee (Ionizing Radiation Group)
Future plan
• Test and validate the Monte Carlo simulation by comparing between calculated and experimental calibration factors.
• Tune the Monte Carlo code for the absolute measurements of activity by the ion chamber.
• Use the Monte Carlo calculation to provide calibration services to the radiopharmaceutical industry.