Skin Model and its impact on Digital Mammography Rodrigo T . Massera; Alessandra Tomal Institute of Physics "Gleb Wataghin ” 1 University of Campinas Campinas, Brazil
Outline • Mammography • Dosimetry – Mean Glandular Dose Motivation • Implemented Models • How? Methodology • MGD vs Skin Model • Differences Results • Summary Conclusions 2
Introduction Why is dosimetry important in mammography? Population-based screening programs Use Ionizing Radiation Quality Control and Optimization 3
Mean Glandular Dose (MGD) Real Breast Incident Photons Skin Glandular Tissue Adipose Tissue
Mean Glandular Dose (MGD) Real Breast Energy Deposited: Glandular Tissue Directly measured? Monte Carlo simulation Skin Glandular Tissue Adipose Tissue
Mean Glandular Dose (MGD) Parameters to consider... • X-ray spectrum; • Geometric Model; Previous Estimations: • Breast Thickness; • Breast Composition ( 𝑔 ); • 5 mm Adipose Tissue ( Dance 1990) • Skin Model? • 4 mm Skin Tissue (Wu 1991/Boone 1999) 64% thinner Credits: Boone & Hernandez 2016, AAPM. “ Changing Perceptions and Updated Methods for Mammography Dosimetry ” Current Measures: Using breast-CT: ≈1.44 mm ( Vedantham et al 2012) ≈ 1.45 mm (Huang et al 2008); 6 + adipose layer
Objectives Study the impact of skin models on Mean Glandular Dose in Digital Mammography Adapt MC • Geometry Code • MGD calculus Analysis • MGD X Skin Models 7
Outline • Mammography • Dosimetry – Mean Glandular Dose Motivation • Implemented Models • How? Methodology • MGD vs Skin Model • Differences Results • Summary Conclusions 8
Methodology 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) 9
Methodology Breast Model* • t = 2 cm – 8 cm • Glandularity ( 𝑔 ) = 1%-100% 10 *Compositions from Hammerstein et al 1979
Methodology 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; 11 *Compositions from Hammerstein et al 1979
Mean Glandular Dose (MGD) Monte Carlo Simulations How do we separate the deposited energy between tissues? penEasy: 𝐹 𝑏𝑤 Skin Homogeneous Glandular- Adipose Tissue Mixture Adipose Tissue 12
Mean Glandular Dose (MGD) MGD Weighing method (Dance 1990) Interaction (I) Simulation Ends: Simulation starts: Type Return 𝐹 𝑚𝑏𝑜𝑒 𝐹 𝑚𝑏𝑜𝑒 =0 (III) Incoherent Photoelectric 𝐹 𝑚𝑏𝑜𝑒 MGD = 𝑁𝑏𝑡𝑡 × 𝑔 (II) 𝑁𝐻𝐸 nMGD = 𝐿 𝑏𝑗𝑠 13
Code modifications... Dosimetry 𝑁𝐻𝐸 nMGD = 𝐿 𝑏𝑗𝑠 Air Kerma from Primary MGD Photons 14 ~40.000 simulations
Automatization with Python™ Windows/Linux full compatibility User Input Python Parallel Simulations Script • Mono/Poly; • Energy Range/Anode Filter; • Breast Thickness range; List of Simulations • Breast Composition; • Skin Model; • Detector Type; PENELOPE • Antiscatter Grid Model; • etc ~40.000 simulations Data Collection Python and saving Return Data 15
Automatization with Python™ 3-10 min/simulation – Uncertainty (1 - 0.25%) Processor i7 7700 3.6 Ghz 16
Outline • Mammography • Dosimetry – Mean Glandular Dose Motivation • Implemented Models • How? Methodology • MGD vs Skin Model • Differences Results • Summary Conclusions 17
Results - Code Validation AAPM – Report 195 (2015) <1% 18
Results - Code Validation <4% Sarno et al 2016 - PMB • 5 cm thick; • 20% 𝑔 ; • 1.45 mm skin; 19
Results: Skin shielding models Monoenergetic Beam 1% 𝑔 100% 𝑔 20 20
Results: Skin shielding models Monoenergetic Beam – Depth Dose 18 keV 20% 𝑔 2 cm breast 8 cm breast 21
Results: Skin shielding models Polyenergetic Beam 20% 𝑔 2 cm 8 cm 16% 15% 36% 34% 22
Results: Skin shielding models Mo/Mo 28 kV Polyenergetic Beam 2 cm breast 21% 23% 23
Results: Skin shielding models Mo/Mo 28 kV Polyenergetic Beam 1% 𝑔 21% 24 17%
Results: Summary Polyenergetic Beam – Skin Models 25
Outline • Mammography • Dosimetry – Mean Glandular Dose Motivation • Implemented Models • How? Methodology • MGD vs Skin Model • Differences Results • Summary Conclusions 26
Conclusions • The Skin Model has a significant impact on MGD estimates; • Skin model affects the MGD up to 37%; • Larger variations: low energies; high glandularity, thin breasts Depth Dose : skin attenuation and Homogeneous Mixture Volume MGD Variation Skin • Reduce the uncertanties; Model 𝑔 (≈50%) • Patient-specific dosimetry; Breast (≈40%) Thickness • Heterogeneous breast (≈350%) Tube Potential Anode/Filter (≈130%) (≈90%) 27
Acknowledgement 28 • Process 2016/15366-9 Process 2015/21873-8 • • Process 483170/2015-3 Lab Members and Alumni Collaborators José Maria Rodrigo T . Massera Bruno L. Rodrigues Fernandez-Varea
Our Institution Funded in 1966 Credits: Lucas Rodolfo de Castro Moura - 29 http://www.lrdronecampinas.com.br/ University of Campinas (UNICAMP): 1st in Latin America
Thank You! atomal@ifi.unicamp.br rmassera@ifi.unicamp.br Rodrigo T . Massera MSc Student IFGW - UNICAMP 30
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