Skin Model and its impact on Digital Mammography Rodrigo T. Massera; Alessandra Tomal Institute of Physics "Gleb Wataghin University of Campinas Campinas, Brazil 1
Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 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 Adipose Tissue Glandular 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; Breast Thickness; Breast Composition (f g ); Skin Model? Previous Estimations: 5 mm Adipose Tissue ( Dance 1990) 4 mm Skin Tissue (Wu 1991/Boone 1999) Credits: Boone & Hernandez 2016, AAPM. Changing Perceptions and Updated Methods for Mammography Dosimetry Current Measures: 64% thinner Using breast-ct: 1.44 mm (Vedantham et al 2012) 1.45 mm (Huang et al 2008); + adipose layer 6
Objectives Study the impact of skin models on Mean Glandular Dose in Digital Mammography Adapt MC Code Analysis Geometry MGD calculus MGD X Skin Models 7
Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 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 (f g ) = 1%-100% *Compositions from Hammerstein et al 1979 10
Methodology Breast Model* t = 2 cm 8 cm Glandularity (f 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? Skin peneasy: E avg Homogeneous Glandular- Adipose Tissue Mixture Adipose Tissue 12
Mean Glandular Dose (MGD) MGD Weighing method (Dance 1990) Simulation starts: E gland =0 (I) (III) Photoelectric Interaction Type Simulation Ends: Return E gland Incoherent MGD = E gland Mass f g (II) nmgd = MGD K air 13
Code modifications... Dosimetry nmgd = MGD K air MGD Air Kerma from Primary Photons ~40.000 simulations 14
Automatization with Python Windows/Linux full compatibility 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 PENELOPE Parallel Simulations ~40.000 simulations Return Data Python Data Collection and saving 15
Automatization with Python 3-10 min/simulation Uncertainty (1-0.25%) Processor i7 7700 3.6 Ghz 16
Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 17
Results - Code Validation AAPM Report 195 (2015) <1% 18
Results - Code Validation Sarno et al 2016 - PMB <4% 5 cm thick; 20% f g ; 1.45 mm skin; 19
Results: Skin shielding models Monoenergetic Beam 1% f g 100% f g 20
Results: Skin shielding models Monoenergetic Beam Depth Dose 18 kev 20% f g 2 cm breast 8 cm breast 21
Results: Skin shielding models Polyenergetic Beam 2 cm 8 cm 20% f g 15% 16% 36% 34% 22
Results: Skin shielding models Polyenergetic Beam Mo/Mo 28 kv 2 cm breast 21% 23% 23
Results: Skin shielding models Polyenergetic Beam Mo/Mo 28 kv 21% 1% f g 17% 24
Results: Summary Polyenergetic Beam Skin Models 25
Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 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 f g ( 50%) Breast Thickness ( 350%) Skin Model ( 40%) Reduce the uncertanties; Patient-specific dosimetry; Heterogeneous breast Anode/Filter ( 90%) Tube Potential ( 130%) 27
28 Acknowledgement Process 2016/15366-9 Process 2015/21873-8 Process 483170/2015-3 Lab Members and Alumni Collaborators Rodrigo T. Massera Bruno L. Rodrigues José Maria Fernandez-Varea
Our Institution Funded in 1966 Credits: Lucas Rodolfo de Castro Moura - http://www.lrdronecampinas.com.br/ 29 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