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8/11/2019 Characterization Protocol
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Department of Medical Physics (051) 405 3156
Characterization of small megavoltage
photon beams for radiotherapy
M.Med.Sc. Project Candidate: IE SETILO
Study leader / Promoter: Dr. F.C.P du Plessis
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INTRODUCTION
Literature fields less than 3x3 cm
Mainly used in stereotactic radiosurgery and IMRT
Fields provide sharp dose gradients, thus less dose spillage
to neighbouring organs
Inaccurate doses given for small fields
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INTRODUCTION
Characterized by LED Lack of LEE result in decrease of dose
Compton Effect
=
Detectors physical density equivalent to water
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INTRODUCTION
Gafchromic film (EBT2)
Small needle-like active particles (1-2m in diameter
and 15-25m in length) composed of LiPDCA
24 hour post-irradiation waiting period prior to scanning
Layer
Nominal
thickness
(m)
Density
(g/cm)
Composition (Atom %)
H Li C O Al
Smooth polyester film
base50 1.35 36.4% 0.0% 45.5% 18.2% 0.0%
Acrylic adhesive 20 1.2 57.1% 0.0% 33.3% 9.5% 0.0%
Active layer (assumes
7.5% moisture)
28 1.2 56.8% 0.6% 27.6% 13.3% 1.6%
Smooth polyester film
base
175 1.35 36.4% 0.0% 45.5% 18.2% 0.0%
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INTRODUCTION
Kodak X-omat V2 film Composed mostly of silver bromide
Small crystals, high spatial resolution
Strong energy dependence
Effective atomic number of 42.6 Over respond
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INTRODUCTION
Ionization chamber, CC01 0.01 cm volume of air, length of chamber 3.6mm with
inner diameter of 2.0mm
Effective atomic number > 13
Small volume of air (less volume averaging)
Good stability and linear response to absorbed dose
Relatively independent of radiation direction
Independent of beam quality-response
Traceable to primary calibration standards
2 mm
Volume: 0.01 cubic centimeters
Sensitivity: 0.0033 nC/cGy
Active length: 3.6 mm
Inner diameter: 2.0 mm
Wall: C552, 0.5 mm thick, 88 mg/cm
Electrode: steel, 0.35 mm diameter
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INTRODUCTION
Ushielded diode (USD) High atomic number, manufactured with very small
sensitive volumes
Active area diameter 2.0mm, active area thickness of
0.06mm Effective atomic number of 14
Better penumbra measurement
High sensitivity compared to pin point ion chamber
Directional dependence Long-term irreversible radiation damage
5mm
Effective Measurement Point:
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INTRODUCTION
EBT2 X-OMATV CC01 EFD
Physical density 1.2 g/cm 2.3 g/cm,
effective
thickness
of 0.2m
0.001
g/cm
2.3 g/cm
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AIM
Characterize small fields using different detectors atdifferent source surface distance using 6, 10 and 15MV
photon beams
Characterize, measure: Beam profiles (field size and Penumbra)
Percentage depth dose curves (PDD)
Total scatter factors (output factors)
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MATERIALS
Linac
Synergy S, capable of producing 6, 10 and 15MV photon
beams at different depths (90cm, 95cm, 100cm & 150cm)
Detectors
Gafchromic film
Ushielded diode
Ionization chamber
Kodak X-omat V2 film
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Films: Use RW3 water equivalent polystyrene plates
(0.1mm thickness tolerance)
Other detectors: Scanditronix/Wellhfer
Blue Phantom Water Tank (0.5mm per axis positional
accuracy and 0.1 mm positional reproducibility)
MATERIALS
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STATISTICAL ANALYSIS
Measurements will be repeated accordingly for eachdetector, in order to determine the mean and standard
deviation of acquired results
Accepted results for beam profile, pdd and output factorwill be the average of all four detectors
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PROGRESSION TREE
Water tank andRW3
measurements
EBT2 film
KodakXV film USD Pinpoint CC01
chamber
90, 95, 100 and 110cm1x1 to 5x5 cmfields
6, 10 and 15MV
BeamprofilesPDD
Outputfactors
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TIME SCHEDULE
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BUDGET
Elekta Synergy S Linac Available
Gafchromic EBT2 film Available
Kodak XV film **
Ionization chamber Available
Unshielded Diode Chamber Available but without its reference
chamber
Water tank Available
RW3 Available
Computer analysis Available
Printing equipment Available
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STUDY LEADER: DR F.C.P DU PLESSIS Acted as examiner for the following
PH.D. Thesis for candidate Inyang, Samuel Okon on Monte Carlo
Simulation of Irregular Electron Fields Using EGSnrc, 2006
M. Tech dissertation for candidate Dierdre Long on An analysis of dose
effectiveness and incidence of lateral rectal complications of high dose-
rate brachytherapy in the radical treatment of cervical cancer, 2007
M. Tech dissertation for candidate Marissa Jordaan on An evaluation of
two immobilization devices for head and neck radiation therapy at theUniversitas annex, Bloemfontein, 2008
M. Tech dissertation for candidate B Kinsella on The development of a
radiation quality control manual by analysing the prevalence of adverse
indicidents during radiation therapy at the Universitas Annex,
Bloemfontein, 2008
PH.D. Thesis for candidate M E Sithole for the PhD defree on the The
Effect of Silicone Gel Breast Prosthesis On Photon Dose Distributions,
2009
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STUDY LEADER: DR F.C.P DU PLESSIS Acted as co- / study leader / promotor for the following candidates:
D. Tech dissertation for candidate G J van der Walt on Radiation field
shaping through low temperature thermal-spray in radiotherapy, 2009
MSc (Med) dissertation for candidate C Trauernicht on Characterization of
a 6 MV photon beam in terms of primary and scatter dose components,
2009
Mr Willie Shaw: Evaluation of a treatment planning system against Monte
Carlo simulated 3D dose distributions. (M.Med.Sc. 20042007) Dr Kobus van der Walt: Radiation field shaping through low temperature
thermal spray. (D Tech. 2005 - 2008)
Dr Omer Aziz Ali: Characterization of electron beams transported through
a photon multileaf collimator for use in optimized modulated electron
radiation therapy procedures (Ph.D. 20072009)
Mrs Dedri OReilly: Megavoltage image reconstruction using cone beam
techniques. (M.Med.Sc. 20082010)
Mr Chris Trauernicht: I131Brachytherapy seed modelling using Monte
Carlo methods (Ph.D. 20102012)
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STUDY LEADER: DR F.C.P DU PLESSIS
Acted as co- / study leader / promotor for the following candidates:
Mr. Cobus Smit: Development and Validation of an X-ray Source Model
for an Elekta Precise Multileaf Collimator to be used in Monte Carlo dose
calculations (M.Med.Sc 2010 - 2013)
Mrs. Dete Liebenberg: Development and Validation of an X-ray Source
Model for an Elekta Precise Multileaf collimator to be used in Monte Carlo
dose calculations (M.Med.Sc 2012 -present) Ms. K.R. Fourie: Electron Field Shaping through Woods alloy end-
frames in radiotherapy, (M.Med.Sc 2011 - 2013)
Mr. L.J. Strauss: IMRT dose verification using Monte Carlo simulations
for a Xio TPS (M.Med.Sc 20122014)
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STUDY LEADER: DR F.C.P DU PLESSIS
Authored & co-authored the following article publications:
Ali, O.A., Willemse, C.A., Shaw, W., OReilly, F.H.J., du Plessis, F.C.P.,
2011. Monte Carlo electron source model validation for an Elekta Precise
linac. Medical Physics 38, 23662373.
du Plessis, F.C.P., Leal, A., Stathakis, S., Xiong, W., Ma, C.-M., 2006.
Characterization of megavoltage electron beams delivered through a
photon multi-leaf collimator (pMLC). Physics in Medicine and Biology 51,21132129.
du Plessis, F.C.P., Willemse, C.A., 2003. Monte Carlo calculation of
effective attenuation coefficients for various compensator materials.
Medical Physics 30, 25372544.
du Plessis, F.C.P., Willemse, C.A., 2005. Radiological properties of a wax
gypsum compensator material. Medical Physics 32, 12461255.
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STUDY LEADER: DR F.C.P DU PLESSIS
Authored & co-authored the following article publications:
du Plessis, F.C.P., Willemse, C.A., 2006. Inclusion of compensator-
induced scatter and beam filtration in pencil beam dose calculations.
Medical Physics 33, 28962904.
du Plessis, F.C.P., Willemse, C.A., Lotter, M.G., Goedhals, L., 1998. The
indirect use of CT numbers to establish material properties needed for
Monte Carlo calculation of dose distributions in patients. Medical Physics25, 11951201.
du Plessis, F.C.P., Willemse, C.A., Lotter, M.G., Goedhals, L., 2001.
Comparison of the Batho, ETAR and Monte Carlo dose calculation
methods in CT based patient models. Medical Physics 28, 582589.
Fan, J., Li, J., Chen, L., Stathakis, S., Luo, W., du Plessis, F.C.P., Xiong,
W., Yang, J., Ma, C.-M., 2006. A practical Monte Carlo MU verification
tool for IMRT quality assurance. Physics in Medicine and Biology 51,
25032515.
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