Chandler Lane Chapman

Thermoluminescence Energy Factor, K(E), for Varying Energies With and

Without the Flattening Filter. TG-51 Pre- and Post-Addendum

MedicalRadiationResearchCenter

La Crosse Wisconsin

October 24, 2014

Introduction and Background TLDs Ionization Chambers TG-51 Use of these devices and protocols for this experiment.

Problem/Hypothesis Assumptions Methods and Materials Initial Set-up TLD Handling- Annealing Process and Chip Factor Analysis.

Data K(E) values TG-51 lead foil vs. no lead foil in 10 MV and 10 MV FFF.

Conclusion

2

Outline

Valence Band

Conduction Band

Crystall ine dielectric material containing impurit ies (activators) that enable it to have thermoluminescence properties.1

Energy -level Diagram of TL process

3

IntroductionThermoluminescence

Conduction Band

Valence Band

ETD

HTDHole Trap + Lum. Center

Heat

ing

ETD

HTD

hν

Ioniz

ation

1. Attix, Frank H. “Introduction to Radiological Physics and Radiation Dosimetry” Chpt. 14

4

IntroductionThermoluminescence

Randall-Wilkins Theory- Describing glow curves

1. Attix, Frank H. “Introduction to Radiological Physics and Radiation Dosimetry” Chpt. 14

Four properties to an ionization chamber Collector Electrode

Shell

Guard

Electrometer

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IntroductionIonization Chambers

Picture courtesy of Dr. Larry DeWerd from AAPM Summer School, Ionization Chambers.

Dose Calculation: raw measurement and correction factors

Recombination effects are corrected using Pion

Ppol effects based on whether you are measuring the collection of positive or negative ions

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Introduction Ionization Chambers

TG-51 -clinical reference for dosimetry calculation for external beam radiation

Based on absorbed dose calibration in water for 60Co

Uses ion chambers as the basis for the measurements Correction factors are necessary: Pion, kenv, Ppol, Pelec

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IntroductionTG-51

Additionally, the addendum accounts for Pleak, Prp

1mm lead foil is to account for electron contamination

TG-51 results in a precise measure of the dose in water with beam quality Q at 10cm depth and dmax

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IntroductionTG-51

Calculate the K(E) values for TLD measurements from 6 mV, 6FFF, 10 mV, 10 FFF beam energies in a 10x10 field size at 10 cm depth

Performed TG-51 on the Clinical TrueBeamTM to calculate the dose given to a set of TLDs at the given energies

Irradiated TLDs using 60Co to obtain 60Co dose reading from the TLDs

Examine the differences between TG-51 and its addendum by comparison of kQ values

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IntroductionUse of These Devices and Protocols in this Experiment.

Introduction and Background TLDs Ionization Chambers TG-51 Use of these devices and protocols for this experiment.

Problem/ Hypothesis Assumptions Methods and Materials Initial Set-up TLD Handling- Annealing Process and Chip Factor Analysis.

Data K(E) values TG-51 lead foil vs. no lead foil in 10 MV and 10 MV FFF.

Conclusion

10

Outline

Currently K(E) values are assumed to be the same for beam energies WFF and FFF.

Due to lower energy spectrum of FFF there is reason to assume these energy correction factors are different.

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Problem/Hypothesis

0 5 10 15 20 25 30 35 400.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

10 x 10 Percent Depth Dose Curves

Depth (cm)

Dos

e (n

orm

aliz

ed to

10

cm d

epth

)

Measured 6FFFMeasured 6MVMeasured 10MVMeasured 10FFF

1 Graph courtesy of Megan Wood.

Compare the TLD energy correction factors of WFF beams and FFF beams. Specifically between 6MV and 6MV FFF as well as 10MV and 10 MV

FFF.

Energy Correction Factor K(E) is defined to be

Compare the values of kQ from TG-51 with and its modifications in TG-51 addendum.

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Specific Aims

TG-51 calculations for K(Q) values are accurate for energies WFF and FFF

TLD chip factor reproducibility is within tolerance range of 2.5% as measured in March1 and checked in June

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Assumptions

1 Initial chip factors measured by Megan Wood and Eric Simiele in March, 2014.

Introduction and Background TLDs Ionization Chambers TG-51 Use of these devices and protocols for this experiment.

Problem/Hypothesis

Assumptions

Methods and Materials Initial Set-up TLD Handling- Annealing Process and Chip Factor Analysis.

Data K(E) values TG-51 lead foil vs. no lead foil in 10 MV and 10 MV FFF.

Conclusion14

Outline

15

Methods and Materials

Annealing• 400°C for one hour.• 80°C for a day.

Ionizing Radiation

Read out• Up to ~350°C• At 150°C half life in days• 200-225°C half life ranges from months to

years

Sort

1. TLD Temp./Time graph courtesy of Attix, Frank H. “Introduction to Radiological Physics and Radiation Dosimetry” Chpt. 142. TLD tray courtesy of Stephanie Junell Determination of the Energy Correction Factor for TLD-100 in 6 and 10 MV photon

beams relative to 60Co

TLD paddles made of Virtual WaterTM

Sealed with water tight O-ring

Place at 10 cm depth in water

TLDs irradiated by 6MV, 6FFF, 10MV, 10FFF

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Set up/ Materials

1. TLD tray courtesy of Stephanie Junell Determination of the Energy Correction Factor for TLD-100 in 6 and 10 MV photon beams relative to 60Co

Introduction and Background TLDs Ionization Chambers TG-51 Use of these devices and protocols for this experiment.

Specific Aim Assumptions Methods and Materials Initial Set-up TLD Handling- Annealing Process and Chip Factor Analysis.

Data K(E) values TG-51 lead foil vs. no lead foil in 10 MV and 10 MV FFF.

Conclusion

17

Outline

18

Dif ference in KE values for beam energies with FF and FFF

Beam Energy K(E) Values ratio % diff.

6FFF 0.920

0.999 0.13%

6MV 0.921

10FFF 0.919

0.994 0.63%

10MV 0.913

Insignificant % difference in K(E) values

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Data

Comparing 10MV beam with lead foil filter to reduce electron contamination to 10 MV with out lead foil. Both KQ values taken in June.

KQ 10 MV w/out Pb 0.9819

KQ 10 MV w/ Pb 0.9811

ratio 0.9992

% difference 0.0849%

<.1%

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Comparing Pre- and Post - Addendum TG51 measurements .

1 Pre-Addendum values courtesy of Megan Wood and Eric Simiele in March, 2014.

KQ Pre‐ Add.

KQ equationPost‐ Add.

KQ Post‐Add. with Pb. 1mm Foil

% Differencewith and without kQequation

%diff w/Lead Foil

6FFF 0.999 0.9971 0.9960 0.19% 0.11%

6 MV 0.996 0.9931 0.29%

10 FFF 0.990 0.9859 0.9857 0.42% 0.02%

10 MV 0.987 0.9819 0.9811 0.52% 0.08%

Introduction and Background TLDs Ionization Chambers TG-51 Use of these devices and protocols for this experiment.

Specific Aim Assumptions Methods and Materials Initial Set-up TLD Handling- Annealing Process and Chip Factor Analysis.

Data K(E) values TG-51 lead foil vs. no lead foil in 10 MV and 10 MV FFF.

Conclusion

21

Outline

Insignificant % difference in the TLD K(E) factor for specific energies with and with out the flattening filter.

Change in KQ was insignificant for FFF beams with and without the lead foil.

Pre- and Post- Addendum showed less than .5% difference for all beams. It may make more of a difference for 10MV

Future Work Energy corrections for other detectors

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Conclusion

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Thank You So Very Much.

Can I answer any questions?

MeganDr. DeWerd and WesSamEricManik

All the calibration clients that helped fund my research