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Evaluation of the absorbed dose reporting mode
of the AAA and AXB algorithms and the Monte-
Carlo code GATE/GEANT4 in high and low density
media
Tony Younes (a,b,c), PhD Student
Alexia Delbaere (a), M. Chauvin(b), L. Simon(a,b), Georges Fares (c),
Laure Vieillevigne (a,b)
a) Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse Oncopole
b) CRCT UMR 1037 INSERM Team15
c) Mount Lebanon Hospital
1
2
Durant les cinq dernières années :
Je ne déclare aucun lien d’intérêt.
Déclaration Publique d’Intérêts
Introduction
Stereotactic Body Radiation Therapy (SBRT)
Hypofractionation
3
Small fields
≤ 3 × 3 cm2
Lateral electronic equilibrium
Reduced fraction
number (1-5)High absorbed dose
(6-30 Gy)
+++
Accuracy on absorbed dose
calculation
Dose report mode
4
AAA
CTElectron density correction
≠Tissue composition ✗
Acuros XB
CT (HU)Mass Densitymaterial assignment
Material library
5 biological materials ICRP 75
16 non biological materials
Dm :Tissue composition ✓ (Not explicitly)
Dm 𝐷𝑤𝐴𝑋𝐵 = 0
∞𝑑𝐸 4𝜋 𝑑
Ω𝜎𝐸𝐷𝑒 𝑟,𝐸
𝜌 𝑟Ψ𝑒 𝑟, 𝐸, Ω
Monte Carlo
Detailed transport
Dm : Tissue composition ✓ (Explicitly if elemental compositions are known)
Dm𝐷𝑤𝑀𝐶 = 𝐷𝑚
𝑀𝐶 ×( 𝑆 𝜌)𝑤
( 𝑆 𝜌)𝑚
𝜙𝑤 ≈ 𝜙𝑚 (Siebers et al. 2000)
Small Watervolume in
medium
Siebers J V,et al Converting absorbed dose to medium to absorbed dose to water for Monte Carlo based photon beam dose
calculations Phys. Med. Biol. 45 983–95 (2000)
Problematic
Dw
Historical clinical experience
Protocols/measurements are based on Dw
5
Dm
Inherently calculated by MC
Converting Dm Dw adds additional absorbed dose uncertainty
Aim
Evaluate dose calculation algorithms against Monte-Carlo simulations and experimental measurements
AAA Dw ?≡? AXB Dw ?≡? MC Dw
vs
Materials and Methods
Experimental configurations
True Beam STx
6 MV WFF photons
MLC Field size: 3 × 3 𝑐𝑚2
EBT3 Films at different depths
Phantom
RW3 (98% polystyrene+ 2% TiO2): 𝜌 = 1.045 𝑔/𝑐𝑚3
Gammex LN300 Lung: 𝜌 = 0.29 𝑔/𝑐𝑚3
Gammex SB3 Cortical Bone: 𝜌 = 1.82 𝑔/𝑐𝑚3
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Gammex SB3CorticalBone1.82g/cm3
3cm
7cm
12cmRW31.045g/cm3
RW31.045g/cm3
Gammex LN300Lung0.29g/cm3
RW31.045g/cm3 4cm
6cm
12cmRW31.045g/cm3
PDD
Materials and Methods
Monte Carlo simulations
6 MV WFF VARIAN Phase Space Files (Constantin et al. 2011)
Modeling of the HD120 MLC and validation (vs PDD, profiles and OF measurements)
Modeling of the experimental phantoms
Simulation parameters
Pcut=1 keV
Ecut =1-10 keV depending on the material
Grid size: 1 × 1 × 1 𝑚𝑚3
Livermore physics list
Dose Actor
Number of particles Uncertainty<1%
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VARIAN phase space
Field specific phase space
Constantin et al. 2011. “Modeling the TrueBeam Linac Using a CAD to Geant4 Geometry Implementation: Dose and
IAEA-Compliant Phase Space Calculations.” Med. Phys. 38(July):4018–24.
Heterogeneity
Plastic Water
Plastic Water
Materials and Methods
8
Comparison Dm
Composition impact
GATE simulation with AXB compositions
vs
AXB
RW31.045g/cm3
Gammex Lung0.29g/cm3
RW31.045g/cm34cm
6cm
12cm RW31.045g/cm3
Gammex CorticalBone1.82g/cm3
RW31.045g/cm33cm
7cm
12cmPolystyrene AXB1.045g/cm3
LungAXB0.29g/cm3
Polystyrene AXB1.045g/cm34cm
6cm
12cm Polystyrene AXB1.045g/cm3
CorticalBone AXB1.82g/cm3
Polystyrene AXB1.045g/cm33cm
7cm
12cm
GATE simulation with Gammexcomposition (experimental)
vs
AXB
Comparison Dw
AAA, AXB and GATE vs
Calibrated in Water𝑫𝒘
𝒎𝒆𝒂𝒔 Epson 10000 XL
Chemical
elementLungAXB
Lung
GammexBoneAXB
Bone
Gammex
H(1) 0.101278 0.0743 0.047234 0.0266
C(6) 0.10231 0.5786 0.14433 0.3034
N(7) 0.02865 0.0196 0.04199 0.0099
O(8) 0.757072 0.2071 0.446096 0.3908
Na(11) 0.00184
Mg(12) 0.00073 0.0022 0.0041
Si(14) 0.0077
P(15) 0.0008 0.10497
S(16) 0.00225 0.00315
Cl(17) 0.00266 0.0008 0.0004
K(19) 0.00194 0.1119
Ca(20) 0.00009 0.20993 0.2648
Ti(22)
Fe(26) 0.00037
Zn(30) 0.00001 0.0001
Chemical
elementLungAXB
Lung
GammexBoneAXB
Bone
Gammex
H(1) 0.101278 0.0743 0.047234 0.0266
C(6) 0.10231 0.5786 0.14433 0.3034
N(7) 0.02865 0.0196 0.04199 0.0099
O(8) 0.757072 0.2071 0.446096 0.3908
Na(11) 0.00184
Mg(12) 0.00073 0.0022 0.0041
Si(14) 0.0077
P(15) 0.0008 0.10497
S(16) 0.00225 0.00315
Cl(17) 0.00266 0.0008 0.0004
K(19) 0.00194 0.1119
Ca(20) 0.00009 0.20993 0.2648
Ti(22)
Fe(26) 0.00037
Zn(30) 0.00001 0.0001
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Results: AXB Dm vs GATE Dm
Gammex compositions
≠ 2.4% Lung
≠2% Bone
AXB compositions
In medium≠<1%
At interface ≠<1.5%
Results: Dw reports Lung case
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Vs Films Plastic Water
1.045 g/cm3
Lung
0.29 g/cm3
Plastic Water
1.045 g/cm3
AAA 1.8% 1.4% 3.1%
AXB Dw 0.6% 0.9% 1.5%
GATE Dw (AXB
compositions)0.8% 1.2% 1%
GATE Dw
(Gammex
compositions) 1.1% 0.5% 0.7%
Results: Dw reports bone case
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Vs Films Plastic Water
1.045 g/cm3
Bone
1.82 g/cm3
Plastic Water
1.045 g/cm3
AAA 1.3% 1.8% 2.5%
AXB Dw 0.3% 9.2% 0.7%
GATE Dw (AXB
compositions)1.1% 3.5% 1.5%
GATE Dw
(Gammex
compositions)
0.6% 4.7% 0.8%
Discussion: Conversion Dw/Dm
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Siebers et al. : 𝜙𝑤 ≠ 𝜙𝑚
𝐷𝑚𝑀𝐶 ×
( 𝑆 𝜌)𝑤
( 𝑆 𝜌)𝑚
𝐷𝑚𝑀𝐶 ×
( 𝑆 𝜌)𝑤
( 𝑆 𝜌)𝑚×
𝜙𝑤
𝜙𝑚
Clinical impact++
Lung Bone
0.2%
0.1%AXB 15%
GATE 10%
0
0,005
0,01
0,015
0,02
0,025
0,03
0,035
0,04
0,045
0,001 0,01 0,1 1
ElectronFluence[cm
-2MeV-
1]
Energy[MeV]
Water AXBLung AXBBone
Conclusion
Evaluation of AAA et AXB:
AXB ≡ MC for similar elemental compositions
AXB > AAA: Lung and after the heterogeneities
Dw reports: AAA, AXB and GATE are not equivalent
In the bone: Measurements ≠ GATE et AXB Dwconversion method should be reviewed.
MC DwFluence correction factor as proposed by Pr. Andreo (Andreo 2015).
13Andreo, P. Dose to ‘water-like’ media or dose to tissue in MV photons radiotherapy treatment planning: still a matter of debate.
Phys. Med. Biol. 60, 309–337 (2015).
14