ionizing radiation group k.b. lee · 2013-10-15 · 22 may 20, 2005 k. b. lee (ionizing radiation...

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]


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


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.


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


IC characterization

Efficiency variation over applied voltage

Efficiency variation over source position


Consistency check


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 %


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


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.


• 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


• 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


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


Geometry

8R vial geometry (in cm)IC geometry (in mm)


IC and vial simulated


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)


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


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.

ionizing radiation group k.b. lee · 2013-10-15 · 22 may 20, 2005 k. b. lee (ionizing radiation...

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