characterization protocol

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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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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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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characterization protocol

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