Skin Model and its impact on Digital Mammography Rodrigo T . - - PowerPoint PPT Presentation

Skin Model and its impact on Digital Mammography

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Rodrigo T . Massera; Alessandra Tomal

Institute of Physics "Gleb Wataghin” University of Campinas Campinas, Brazil

Outline

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Motivation

• Mammography
• Dosimetry – Mean Glandular Dose

Methodology

• Implemented Models
• How?

Results

• MGD vs Skin Model
• Differences

Conclusions

• Summary

Introduction

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• Population-based screening programs
• Use Ionizing Radiation
• Quality Control and Optimization

Why is dosimetry important in mammography?

Mean Glandular Dose (MGD)

Adipose Tissue Glandular Tissue

Skin

Real Breast

Incident Photons

Adipose Tissue Glandular Tissue Skin

Real Breast

Energy Deposited: Glandular Tissue Directly measured? Monte Carlo simulation

Mean Glandular Dose (MGD)

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Parameters to consider...

• X-ray spectrum;
• Geometric Model;
• Breast Thickness;
• Breast Composition (𝑔

𝑕);

• Skin Model?
• 5 mm Adipose Tissue ( Dance 1990)
• 4 mm Skin Tissue (Wu 1991/Boone 1999)

Using breast-CT: ≈1.44 mm (Vedantham et al 2012) ≈1.45 mm (Huang et al 2008); + adipose layer

Previous Estimations: Current Measures:

64% thinner

Credits: Boone & Hernandez 2016, AAPM. “Changing Perceptions and Updated Methods for Mammography Dosimetry”

Mean Glandular Dose (MGD)

Objectives

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Study the impact of skin models on Mean Glandular Dose in Digital Mammography

• Geometry
• MGD calculus

Adapt MC Code

• MGD X Skin Models

Analysis

Outline

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Motivation

• Mammography
• Dosimetry – Mean Glandular Dose

Methodology

• Implemented Models
• How?

Results

• MGD vs Skin Model
• Differences

Conclusions

• Summary

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Monte Carlo code:

• PENELOPE (2014) + penEasy (2015)

Beam Parameters:

• Monoenergetic (8 – 60 keV)
• Polyenergetic (22 – 35 kV):
• Mo (Mo-Rh)
• Rh (Rh)
• W (Rh-Al-Ag)

*X-ray spectra from Hernandez et al (2014)

Methodology

Methodology

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*Compositions from Hammerstein et al 1979

Breast Model*

• t = 2 cm – 8 cm
• Glandularity (𝑔

𝑕) = 1%-100%

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Breast Model*

• t = 2 cm – 8 cm
• Glandularity (𝑔

𝑕) = 1%-100%

Skin shielding Models

I. 5 mm adipose; II. 4 mm skin;

• III. 1,45 mm skin;
• IV. 1,45 mm skin + 2 mm adipose;

V. 1,45 mm skin + 3,55 mm adipose; *Compositions from Hammerstein et al 1979

Methodology

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Adipose Tissue Homogeneous Glandular- Adipose Tissue Mixture Skin

Monte Carlo Simulations

How do we separate the deposited energy between tissues? penEasy: 𝐹𝑏𝑤𝑕

Mean Glandular Dose (MGD)

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MGD Weighing method (Dance 1990)

Simulation starts:

𝐹𝑕𝑚𝑏𝑜𝑒=0 Interaction Type

Incoherent

Photoelectric

(I) (II) (III)

Simulation Ends: Return 𝐹𝑕𝑚𝑏𝑜𝑒

MGD =

𝐹𝑕𝑚𝑏𝑜𝑒 𝑁𝑏𝑡𝑡 × 𝑔

𝑕

nMGD =

𝑁𝐻𝐸 𝐿𝑏𝑗𝑠

Mean Glandular Dose (MGD)

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Dosimetry

Air Kerma from Primary Photons

MGD

Code modifications...

nMGD =

𝑁𝐻𝐸 𝐿𝑏𝑗𝑠

~40.000 simulations

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User Input

• Mono/Poly;
• Energy Range/Anode Filter;
• Breast Thickness range;
• Breast Composition;
• Skin Model;
• Detector Type;
• Antiscatter Grid Model;
• etc

Python Script

List of Simulations

Parallel Simulations Windows/Linux full compatibility PENELOPE

Data Collection and saving

Python

Return Data

Automatization with Python™

~40.000 simulations

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Automatization with Python™

3-10 min/simulation – Uncertainty (1 - 0.25%) Processor i7 7700 3.6 Ghz

Outline

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Motivation

• Mammography
• Dosimetry – Mean Glandular Dose

Methodology

• Implemented Models
• How?

Results

• MGD vs Skin Model
• Differences

Conclusions

• Summary

Results - Code Validation

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AAPM – Report 195 (2015)

<1%

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• 5 cm thick;
• 20% 𝑔

𝑕;

• 1.45 mm skin;

<4%

Sarno et al 2016 - PMB

Results - Code Validation

Results: Skin shielding models

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Monoenergetic Beam

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1% 𝑔

𝑕

100% 𝑔

𝑕

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Monoenergetic Beam – Depth Dose 18 keV

20% 𝑔

𝑕

2 cm breast

8 cm breast

Results: Skin shielding models

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Polyenergetic Beam

2 cm 8 cm

20% 𝑔

𝑕

36% 15% 34% 16%

Results: Skin shielding models

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Polyenergetic Beam

Mo/Mo 28 kV

2 cm breast

21% 23%

Results: Skin shielding models

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Polyenergetic Beam

Mo/Mo 28 kV

21% 17%

Results: Skin shielding models

1% 𝑔

𝑕

Results: Summary

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Polyenergetic Beam – Skin Models

Outline

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Motivation

• Mammography
• Dosimetry – Mean Glandular Dose

Methodology

• Implemented Models
• How?

Results

• MGD vs Skin Model
• Differences

Conclusions

• Summary

Conclusions

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𝑔

𝑕 (≈50%)

Breast Thickness (≈350%) Skin Model (≈40%)

MGD Variation

Tube Potential (≈130%)

Depth Dose : skin attenuation and Homogeneous Mixture Volume

Anode/Filter (≈90%)

• Skin model affects the MGD up to 37%;
• Larger variations: low energies; high glandularity, thin breasts
• The Skin Model has a significant impact on MGD estimates;
• Reduce the uncertanties;
• Patient-specific dosimetry;
• Heterogeneous breast

Acknowledgement

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• Process 2016/15366-9
• Process 2015/21873-8
• Process 483170/2015-3

Rodrigo T . Massera Bruno L. Rodrigues José Maria Fernandez-Varea

Lab Members and Alumni Collaborators

Our Institution

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University of Campinas (UNICAMP): 1st in Latin America

Credits: Lucas Rodolfo de Castro Moura - http://www.lrdronecampinas.com.br/

Funded in 1966

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Thank You!

atomal@ifi.unicamp.br rmassera@ifi.unicamp.br

Rodrigo T . Massera MSc Student IFGW - UNICAMP