evaluation of the absorbed dose reporting mode of...

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

[email protected]

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

6

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


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%

7

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


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

9

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

11

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

12

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).

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