NRC-CNRC
The EGSnrc Monte Carlo systemIwan Kawrakow
Ionizing Radiation Standards, NRC, Ottawa, Canada
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Outline
History & Overview
EGSnrc user codes
Brief review of cross sections
Brief review of condensed history implementation
Selected benchmarks
EGSnrc C++ class library
Selected recent EGSnrc applications
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EGSnrcA package for the Monte Carlo simulation of coupledelectron-photon transport
The dynamic range is between 1 keV and several tens of GeVLower energy limit due to large uncertainties in crosssections and the fact that the track concept increasinglylooses validity in the eV rangeUpper energy limit due to lack of radiative corrections, noproduction of pp̄-pairs other than e+e−,Landau-Pomeranchuk effect not taken into account
Elements Z = 1 · · · 100, arbitrary compounds and mixturesusing the independent atom approximation
Uses a class II scheme for the simulation of charged particletransport
Written in Mortran 3
Successor of EGS4
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Major developments
EGS3 – 1970sRichard Ford & Ralph Nelson developed the code for high energy
particle physics at SLAC
EGS4 – 1980sRalph Nelson, Hideo Hirayama (visitor at SLAC) & Dave Rogers (at
NRC) released EGS4, focus shifts to lower energy applications
PRESTA – 1986Alex Bielajew & Dave Rogers (at NRC) improved the condensedhistory transport at low energies. Released as add-on to EGS4
User codes – late 80s, early 90sRogers & Bielajew (and numerous students) developed a series of
user codes relevant for ion chamber dosimetry
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Major developments
Photon cross section improvements – early 1990’sBielajew at NRC and Hirayama, Namito & Ban at KEK improved the
treatment of several photon interaction processes
BEAM – 1995Rogers (and many others at NRC) released BEAM, an EGS4 usercode for the simulation of medical linacs. This is currently the most
widely used code in the Medical Physics community (300+ citations)
Multiple scattering & transport mechanics – 1997Kawrakow & Bielajew published a new multiple elastic scatteringapproach and a new condensed history algorithm that removes
most of the EGS4 limitations
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Major developments
Work on EGSnrc – 1998· · ·2000Kawrakow at NRC incorporated all previous + many new
developments in a new EGS version to become known as EGSnrc
EGS4 not actively maintained – ∼ 1998 · · · presentNot actively maintained (except for the KEK version)
Work on EGS5 – ∼ 1998 · · · presentBielajew, Nelson & KEK group announce plans to develop EGS5,
only a beta release so far
EGSnrc released – 2000Kawrakow & Rogers release EGSnrc, now considered by many to
be the “golden standard” in the Medical Physics community(200+ citations)
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Initial EGSnrc release
All EGS4 extensions included by default
Many subroutines rewritten
Completely new and vastly superior condensed historyimplementation
Kawrakow & Bielajew multiple scattering theory extended toelastic scattering with spin effects taken into account
Compton scattering with binding and Doppler broadening
Improved photo-absorption
Atomic relaxations
Major code clean-up, many bug fixes, algorithm optimizations
New 300 pages manual
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Recent developmentsBEAMnrc – 2001BEAM adapted to work with EGSnrc and renamed BEAMnrc
Electron Impact Ionization – 2002
EGSnrcMP – 2003A new run-time environment that works on Unix/Linux andWindows
DBS – 2004New variance reduction techniques that dramatically improvethe efficiency of linac simulations
egspp – 2005New C++ class library for EGSnrc that provides a geometrypackage, several particle source and many useful utilityclasses. Still under heavy development
Photon cross section improvements – 2006Better treatment of pair production and radiative corrections forCompton scattering
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MC papers in Med.Phys. & PMB
1994 1996 1998 2000 2002 2004 2006year
102
103
Mo
nte
Car
lo p
aper
s
⇒ by 2016 all papers will relate to MC in one way or another
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EGSnrc structure
C++classlibrary
MortranCC++
Mortran
SHOWER
MSCAT
SSCAT
RELAX
Media Data(EGSnrc extensions)
ELECTR
EDGSET
init_compton
inir_spin
init_ms_SR
mscati
MOLLER
ANNIH
BHABHA
BREMS
MSDIST
EGSPHOTON
PAIR
COMPT
PHOTO
RAYLE
UPHI
2
HATCHCODE
MediaData(PEGS4)
BlockData
2 2
2 2
UserControlData
MAIN HOWNEAR HOWFAR
informationextracted
from Shower
AUSGAB
USERCODE
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EGSnrc tutorial user codes
Tutorial codes tutor1...tutor7
Simple hard-coded slab geometrySimple hard-coded particle sourceDemonstrate basic scoring techniques.See PIRS-701 for more details
Tutorial codes tutor2pp, tutor7pp
Same as corresponding tutorials in Mortran but written inC++Can use arbitrary geometry constructible with egspp
Can use any source provided by egspptutor2pp derives from EGS SimpleApplication
tutor7pp uses EGS AdvancedApplication
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EGSnrc RZ user codes
Described in detail in PIRS-702
All implement an RZ-geometry
All provide the same set of common particle sources
Usable via a GUI by Ernesto Mainegra (see PIRS-801)
CAVRZnrc: Calculates the dose to the cavity of an ionizationchamber and correction factors relevant for primary air kermastandards
DOSRZnrc: Scores the dose deposited in all regions. Can alsocompute a pulse height distribution
FLURZnrc: Calculates particle fluence in user defined regions(total and differential in energy)
SPRRZnrc: Calculates stopping power ratios needed in primarystandards and dosimetry protocols
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RZ GUI
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RZ GUI
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Other EGSnrc user codes
g: Computes mass energy transfer/absorption coefficients for agiven photon spectrum
CAVSPHnrc: Same as CAVRZnrc but implements aspherical/conical geometry
EDKnrc: Computes energy deposition kernels needed byconvolution/superposition methods
EXAMIN: Can be used to examine cross section data sets
cavity
Full-featured user code in C++Provides same functionality as CAVRZnrcAny geometry or particle source can be usedCan compute cavity dose simultaneously in severalgeometries
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BEAMnrc & DOSXYZnrcMost widely used codes in the Medical Physics community(300+ citations)
Developed by Dave Rogers & many others at NRC
First version (based on EGS4) released in 1995
Adapted to EGSnrc in 2000
BEAMnrc: simulation of medical linacs and typical X-ray tubes
DOSXYZnrc: dose in a rectilinear geometry (possibly definedvia CT images)
Numerous variance reduction techniques
Maintained and developed by Walters, Kawrakow (NRC) &Rogers (Carleton U)
Extensive manuals: PIRS–509 & PIRS–794
Course ∼once a year (next course October 2–5 in Ottawa)
Both codes have own GUI’s
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Documentation
PIRS–701: main EGSnrc manualnot updated to reflect the recent cross section improvements
PIRS–702: RZ codes manual
PIRS–801: RZ-GUI manual
PIRS–877: EGSnrcMP environment
PIRS–898: C++ class library (egspp) manual
PIRS–509: BEAMnrc manual
PIRS–794: DOSXYZnrc manual
SLAC–265: original EGS4 manual
PIRS–436: History, overview and recent improvements ofEGS4 (outdated)
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Resources
www.irs.inms.nrc.ca/EGSnrc/EGSnrc.html(search for EGSnrc on Google and follow first link)
the EGSnrc distribution site. Includes on-line html and pdf versionsof the manuals, list of known bugs/patches, news, etc.
http://rcwww.kek.jp/research/egs/the EGS home page now maintained at KEK
www.irs.inms.nrc.ca/BEAM/beamhome.html(search for BEAMnrc on Google and follow first link)
the BEAMnrc home page and distribution site
EGS list serverlow volume, main mode for communication with EGS users
(see instructions on EGSnrc or EGS pages how to subscribe)
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Courses
EGSnrc courses every ∼18–24 months; next course ∼October2007?
BEAMnrc courses every ∼12–18 months; last course was Oct2006 in Ottawa
Courses announced under “News” on the EGSnrc page
Next (or possibly previous) course brochures at
www.irs.inms.nrc.ca/papers/egsnrc/brochure.htmlwww.irs.inms.nrc.ca/omega/brochure.html
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EGSnrc Physics
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Photon cross sections
Incoherent (Compton) scattering
Coherent (Rayleigh) scattering
Pair/triplet production
Photo-absorption
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Compton scattering
Theoretical total and differential cross sections: the user has thechoice between
Scattering with free electrons at rest using the Klein-Nishinaformula. This is the same as in EGS4 but the samplingalgorithm has been optimized
Binding effects and Doppler broadening in the relativisticimpulse approximation (default).
The approach used is similar to PENELOPE’sThe necessary Compton profiles are taken from [Biggs et al,Atomic Data and Nucl. Data Tables 16 (1975) 201.]The relaxation cascade of inner shell vacancies created inCompton scattering events is taken into account
New: radiative corrections up to O(α3) can be taken intoaccount
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Rayleigh scattering
Elements: total cross sections from Storm & Israel, XCOM,EPDL–97 or user Bob’s cross sections
Elements: differential cross sections based on atomic formfactors from [Hubbell and Øverbø, J. Phys. Chem. Ref. Data(1979) 69.]
Mixtures: independent atom approximation (known to be notvery accurate!)
TODO list: give the user the option to easily implement and usetheir own molecular form factors
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Pair/triplet productionTotal cross sections from Storm & Israel, XCOM, EPDL–97 oruser Bob’s cross sections
Extreme relativistic first Born approximation with screening(Coulomb corrected above 50 MeV) for the cross sectionsdifferential in energy.
Triplet production is not explicitely modeled but taken intoaccount by adding the triplet total cross section to the pair totalcross section
The angular distribution of electrons and positrons is selectedfrom a modified version of Eq. 3D-2003 of [Motz et al, Rev.Mod. Phys. 41 (1969) 581.] or its leading term.
New: screening corrected exact differential cross sections dueto Olsen, Mork & Øverbø up to 85 MeV
New: explicit simulation of triplet events from the Votruba-Morkcross section (not yet in official release)
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New differential pair cross sections
0 0.2 0.4 0.6 0.8 1positron energy fraction
0
0.5
1
1.5
2cr
oss
sect
ion
in 1
0-4 m
b
1.5 MeV
2.5 MeV 5 MeV
10 MeV
50 MeV (x2)
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Photo-absorption
Total cross sections from Storm & Israel, XCOM, EPDL–97 oruser Bob’s cross sections
For mixtures the interacting element is explicitely sampled
The interacting shell is explicitely sampled usingphoto-absorption branching ratios
The binding energy of the interacting shell is subtracted fromthe photo-electron energy
The relaxation cascade of the shell vacancy is taken intoaccount
The angular distribution of the photo-electrons is picked fromthe Sauter distribution
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Atomic relaxations
In EGSnrc the relaxation cascade of inner shell vacancies is anindependent process that is initiated each time a vacancy iscreated
Currently in photo-absorption, bound Compton scattering,electron impact ionizationFuture: triplet production, electron-electron bremsstrahlung
All shells with binding energies above 1 keV
All radiative and non-radiative transitions to/from K-, LI-, LII-and LIII-shells
All radiative and non-radiative transitions to/from “average” M-and N-shells.
TODO list: remove the above limitation
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Electron/positron cross sections
Bremsstrahlung
Inelastic collisions with atomic electrons
Elastic collisions with nuclei and atomic electrons
Positron annihilation
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BremsstrahlungFor dσ/dk the user has the choice between
The NIST bremsstrahlung cross section data base (basis forICRU radiative stopping powers)Extreme relativistic first Born approximation (Coulombcorrected above 50 MeV) with an empirical correction torecover ICRU radiative stopping powers.
Total bremsstrahlung cross sections for production of photonswith energy greater than a user specified threshold arecalculated from the selected differential cross section
Restricted radiative stopping power for sub-thresholdbremsstrahlung
Angular distribution of bremsstrahlung photons from Eq. (2BS)of Koch & Motz, its leading term, or user Bob’s approach
Work in progress: explicit simulation of electron-electronbremsstrahlung
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Inelastic collisions
Møller (e−) or Bhabha (e+) cross sections for collisions thatresult in the creation of δ-particles with energies greater than auser specified threshold
Continuous-slowing-down approximation using the restrictedcollision stopping power from the Bethe-Bloch theory forsub-threshold processes
Density effect corrections from ICRU–37 or the empiricalSternheimer formula
Electron Impact Ionization for K- and L-shells with bindingenergies above 1 keV. Cross sections from Kawrakow, Casnati,Gryzinski, Kolbenstvedt, or user Bob can be used.
Work in progress: radiative corrections for e+/e− inelasticscattering
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Positron annihilation
Two-photon in-flight annihilation from the first Bornapproximation neglecting binding
Two-photon annihilation at rest
Single- and n-photon (n ≥ 3) annihilation ignored becausecross sections much smaller
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Elastic collisions
User has the choice between
The screened Rutherford cross section with a screening anglefrom the single scattering theory of Moliére. This is the singleelastic scattering cross section effectively used in EGS4 via themultiple scattering theory of Moliére.
The screened Rutherford cross section times the Mott spincorrection factor (which is different for electrons and positrons)with a screening angle selected so that the first elasticscattering moment from PWA cross sections is reproduced.
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Ion chamber response
Early attempts in the ’80s with EGS4 revealed ∼40% variationof the computed cavity dose with electron step size
The PRESTA algorithm released in 1987 greatly reduced theproblem
Rogers demonstrated in 1993 thatEven with PRESTA, there is still ∼2.5% variation of cavitydose with step size for graphite wall chambers in 60CobeamsCalculation does not converge to the expected result in thelimit of short stepsEven larger step-size dependencies in kV beams
Much larger step-size dependencies for chamber walls otherthan graphite (e.g. ∼6% for Al).
Problem finally solved with release of EGSnrc
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Ion chamber response in60Co beams
0.00 0.05 0.10 0.15 0.20 0.25ESTEPE
0.94
0.95
0.96
0.97
0.98
0.99
1.00
1.01
1.02ca
lcu
late
d r
esp
on
se/e
xpec
ted
EGS4/PRESTA, aluminum wall
EGSnrc: both walls
EGS4/PRESTA
graphite wall
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Condensed history aspects
Multiple elastic scattering: exact theory valid for arbitrary stepsizes, both for the screened Rutherford cross section and thecross sections with spin effects taken into account
Electron-step algorithm: most accurate algorithm known(truncation error is O(∆s4))
Evaluation of energy dependent quantities: accurate up toO(∆E4)
Correct implementation of the fictitious cross section method
Single elastic scattering in the vicinity of interfaces betweendifferent materials
⇒ Step-size independent and artifact free simulation at the sub0.1% level.
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Benchmarks
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Benchmark: backscatter coefficients
10-2 10
-110
0 101
electron energy (MeV)
0.00
0.05
0.10
0.15
bac
ksca
tter
co
effi
cien
t
EGSnrc
Al
10-2 10
-110
0 101
electron energy (MeV)
0.0
0.1
0.2
0.3
0.4
0.5
bac
ksca
tter
co
effi
cien
t
EGSnrc
Au
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Benchmark: depth dose curves
0 0.2 0.4 0.6 0.8 1depth/r0
0
2
4
6D
/Φ0 (
10-1
0 Gy
cm2 )
EGSnrcexperiment Lockwood et al
Be
U
1 MeV electrons
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Benchmark: Ge detector response
0 50 100 150 200 250 300E (keV)
0
2
4
6
8
cou
nts
(M
eV-1
)experimentEGSnrc, IAEGSnrc, KN
51Cr source, HPGe detector
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Benchmark: parallel-plate chamber response
0 20 40 60 80Z of back wall
0.90
0.95
1.00
1.05
1.10
1.15
MC
vs
exp
erim
ent
ITSEGS4/PRESTAEGSnrc
Z
Al
air
Co60
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Benchmark: chamber response to90Sr/90Y beta
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charge collection
high voltage
0−12mm
PMMA clamping ring
PMMA
aluminium
active volume
collecting areagraphite−coated
guard ring
graphite−coated hole
PMMA piston
1 2 3 4 5 cm
graphite−coated
Mylar windowgraphite−coated
Mylar µ 2
µ
connector
with graphite wire
connector
2layer (480 g/cm )
(474 g/cm ) ����
cm3.0055
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Benchmark: chamber response to90Sr/90Y beta
10-1
100 10
110
2
additional mylar foil thickness /mg/cm2
1.000
1.025
1.050
1.075
1.100
1.125
1.150
1.175
no
rmal
ized
do
se r
ate
EGSnrcexperiment
90Sr/
90Y beta source
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Benchmark: Elekta 25 MV beame
Target
Primarycollimator
Flatteningfilter
Monitorchamber
Mirror
Secondarycollimation
Fluence plane
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Benchmark: Elekta 25 MV beam
0 5 10 15off-axis distance /cm
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
OA
R
MC, hevimetMC, brassMC, large PMMA experiment, hevimetexperiment, brassexperiment, large PMMA
0 1 2 3 4chamber midpoint (cm)
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
mea
sure
d -
cal
cula
ted
do
se (
% o
f D
max
)
NACPPTW233642
Off-axis ratio in air difference to chamber dose in water
In both cases full simulation of the detectors
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Benchmark: Pancake chamber
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EGSnrc C++ class library(egspp)
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Motivation
A Monte Carlo (MC) simulation requires the description of thegeometry of interest
Some general purpose MC codes (e.g. MCNP, Geant4,PENELOPE) provide powerful geometry packages
Advantage: simulations can be set up quicklyDisadvantage: simulations often run too slow, at leastpartially because of the generality of the geometry routines
In EGSnrc the user has to provide the geometryAdvantage: optimized geometry routines can beprogrammed for the problem of interest. EGSnrc isdistributed with several user codes that provide geometryimplementations for common situationsDisadvantage: if no geometry implementation is available,programming it can be very tedious and time consuming
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Overview
Geometry package
Particle sources
EGS SimpleApplication and EGS AdvancedApplication
Many other utility classes
Described in detail in PIRS–898 (html version only)
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Abstract geometry objects
Every implementation of a model of geometrical structure mustprovide several methods to permit the simulation of particletransport:
−1
0
1
2
3
j′=howfar(j, ~x, ~u, t) t⊥ = hownear(j, ~x) j = isWhere(~x)(EGSnrc specific)
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Concrete geometry objects
“Elementary” geometriesMethods implemented directlyExamples: planes, cylinders, spheres, cones, pyramids,prisms, etc.
Composite geometriesBuilt from elementary or other composite geometriesUse a certain type of logic to put the constituent geometryobjects togetherExamples: envelope geometry, union geometry,transformed geometry, N-dimensional geometry, geometrystack, CD-geometry.
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Example: envelope geometry
isWhere(~x) logic:
If point ~x is outside the box, then return -1
If point ~x is inside the box, but outside thesphere, then return 0
Else return 1
0
1
−1
If point ~x is outside the “envelope”, then return-1
If point ~x is inside the “envelope”, but outsidethe inscribed geometry, then return 0
Else return 1
−1
0
1
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Example: envelope geometry
Logic can be generalized to the situationwhere the “envelope” has many regions, andthere is an arbitrary number of inscribedgeometries
Generalization only requires a predeterminedregion numbering scheme
howfar and hownear also require acompletely generic algorithm that isindependent of the envelope and inscribedgeometries
Only requirements are that all inscribed ge-ometries are completely contained within theenvelope and don’t overlap each other
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Example: N-dimensional geometry
howfar logic:
Calculate all distances ti to the “dimensions” of the geometry
Return Minti
Examples: XYZ, RZ, spheres & cones, spheres & planes, RZΦ, etc.
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Geometry vieweregs view
Geometries are defined in an input file ⇒ need for visualization
Automatic translation of arbitrary complicated geometries in agraphics language (e.g. OpenGL, DirectX) is exceedinglydifficult
⇒ Construct the 3D image using the howfar and isWheremethods provided by each geometry
Disadvantage: much slower than rendering an OpenGLscene (but still fast enough on modern hardware for realtime rotation, transparency, etc.)Advantage: needs the same methods used at run time ⇒
provides additional QA check
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Geometry vieweregs view
screengeometry object
viewer
light
Uses simplest OpenGL light model
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Geometry examples
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Timing benchmarks
Mortran code C++ code Calculation Timing ratio
tutor2 tutor2pp 20 MeV e− on 0.981 mm Ta
cavrznrc cavity 1.25 MeV γ on 1.18 (RZ)pancake chamber 0.97 (Envelope)
BEAMnrc beampp 16 MV photon 0.87 (no VRT)linac 0.89 (RR)
0.36 (DBS + RR)
Simulations use the same physics & VRT’s and are run on thesame computer
⇒ Timing differences due to geometry & scoring
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Utility classes
Classes for sampling from a probability distribution
Classes for handling system-dependent facilities (loading ofshared libraries, timing, etc.)
Classes for run control (including parallel processing)
Scoring classes
Random number generator
Spline and linear interpolations
Reading an input file
Transformations
Etc.
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Recent EGSnrc applications
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Topics of MC papers in 2006
Characterization of irradiation devices:MV linacs, Tomotherapy, X-ray tubes, Gamma- and Cyberknife,Micro beams, Brachytherapy (seeds and miniature X-raytubes), Protons and Ions, etc.
ImagingCBCT, digital radiography, PET, SPECT, dose to imagedpatient, mammography, new X-ray tube designs, indirect CT,scattered X-rays, etc.
IMRT & OptimizationDirect MC optimization, corrections for and comparisons withtraditional optimization methods, new MLC designs, EMRT &MERT, patient motion, etc.
Detector responseEPIDs, phosphor screens, scintillation detectors, CZTdetectors, CdWO4 detectors, etc.
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Topics of MC papers in 2006 (cont’d)
Radiation dosimetrycorrection factors (Pwall, effective point of measurement, etc.),ion chamber design, conversion factors, film dosimetry, etc.
Brachytherapyshielding, seed self-attenuation, new techniques, combinationwith external beams, dosimetric properties and constants, doseescalation near Au seeds, etc.
Dose calculation4D, Comparisons with and improvements of traditionalalgorithms, fast algorithms, verification of commercialimplementations, particle therapy, MC based brachytherapyplanning, dose kernels, neutron capture therapies, etc.
New treatment techniquesconverging stereotactic delivery of kV X-rays, synchrotronradiation, several of the above
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NRC-CNRC
Topics of MC papers in 2006 (cont’d)
Design of new devicesLinacs without flattening filters, Photons and Electron MLC’s,X-ray tubes, Detectors, IMRT with 6060, new integrated deliveryand imaging devices, Laser accelerated protons and electrons,etc.
MiscellaneousDose outside of treatment fields, radiation shielding andprotection, interaction cross sections, efficiency of MCsimulations, dose enhancement due to contrast agents andgold seeds, presence of strong magnetic fields, denoising ofMC computed dose distributions, etc.
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NRC-CNRC
Fast X-ray tube simulations
1×106
2×106
3×106
4×106
5×106
6×106
7×106
Nsplit -1
0.0
2.0×105
4.0×105
6.0×105
8.0×105
1.0×106
1.2×106
1.4×106
1.6×106
rela
tive
effic
ienc
y εD
BS/ε
Monte Carlo data2
nd order polynomial
maximum efficiency gain
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Fast X-ray tube simulations
0.02 0.04 0.06 0.08 0.1 0.12energy /MeV
0.0
0.5
1.0
1.5
2.0
2.5
flu
ence
(1e
-6/M
eV/in
cid
ent
par
ticl
e /c
m-2
MeV
-1)
120 kV spectrum from a BEAMnrc/DBS simulation after 2 min. on asingle 2.66 GHz CPU.
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NRC-CNRC
Free Air Chamber correction factors
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NRC-CNRC
Free Air Chamber correction factors
120 140 160 180 200 220 240 260tube potential / keV
0.990
0.995
1.000
1.005
1.010
total
electron loss
scatter
attenuation
measured: filled symbols MC: open symbols
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NRC-CNRC
Uncertainty analysis
130 140 150 160 170 180 190 200tube potential / keV
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6re
lati
ve d
iffe
ren
ce /
%
no Rayleighno EIISI cross sectionsBH brems. cross sectionsno binding corrections
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NRC-CNRC
CBCT scatter calculations
Can the calculation be done faster?
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NRC-CNRC
Fast CBCT scatter calculationsForced detection for photonstowards screen
Interaction splitting
Russian Roulette for photons awayfrom screen
Delta tracking for photons awayfrom screen
Variable splitting number to guaran-tee similar weights of detected pho-tonsSystematic sampling of primary photons
⇒ ∼300 times faster compared to analog, ∼ 3 × 104 timescompared to full
⇒ 0.1 seconds/projection on modern desktop PC for 15%statistics using 5 mm voxels
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NRC-CNRC
Fast 60Co simulations
Motivation:
Primary air kerma standardCorrection factors have never been computed using arealistic 60Co sourceNumber of particles required is too large to be stored in aphase space file
Recent interest in using 60Co for IMRT60Co IMRT as a cheaper alternative to IMRT with MV linacs60Co source combined with imaging modality such as MRI
⇒ Need for fast generation of particles emerging from the 60Codevice
Approach: Combine directional source biasing with DBS inBEAMnrc/beampp
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NRC-CNRC
Fast 60Co simulations
103 10
4
NBRSPL
100
120
140
160
180
200
220
240
260
280
300
rela
tive
eff
icie
ncy
beampp
BEAMnrc
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Skeletal dosimetry
⇒
See R. Kramer et al, PMB 51 (2006)6265
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