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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
5
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
6
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
7
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
8
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
9
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.
11
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.
12
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
13
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
16
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
19
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%
20
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
22
Conclusion
23
Thank You So Very Much.
Can I answer any questions?
MeganDr. DeWerd and WesSamEricManik
All the calibration clients that helped fund my research