Skin Model and its impact on Digital Mammography

Size: px

Start display at page:

Download "Skin Model and its impact on Digital Mammography"

Milton Potter
5 years ago
Views:

1 Skin Model and its impact on Digital Mammography Rodrigo T. Massera; Alessandra Tomal Institute of Physics "Gleb Wataghin University of Campinas Campinas, Brazil 1

2 Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 2

3 Introduction Why is dosimetry important in mammography? Population-based screening programs Use Ionizing Radiation Quality Control and Optimization 3

4 Mean Glandular Dose (MGD) Real Breast Incident Photons Skin Adipose Tissue Glandular Tissue

5 Mean Glandular Dose (MGD) Real Breast Energy Deposited: Glandular Tissue Directly measured? Monte Carlo simulation Skin Glandular Tissue Adipose Tissue

6 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

7 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

8 Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 8

9 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

10 Methodology Breast Model* t = 2 cm 8 cm Glandularity (f g ) = 1%-100% *Compositions from Hammerstein et al

11 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

12 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

13 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

14 Code modifications... Dosimetry nmgd = MGD K air MGD Air Kerma from Primary Photons ~ simulations 14

Automatization with Python Windows/Linux full compatibility User Input Mono/Poly; Energy Range/Anode Filter; Breast Thickness range; Breast Composition; Skin Model;

15 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 ~ simulations Return Data Python Data Collection and saving 15

16 Automatization with Python 3-10 min/simulation Uncertainty (1-0.25%) Processor i Ghz 16

17 Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 17

18 Results - Code Validation AAPM Report 195 (2015) <1% 18

19 Results - Code Validation Sarno et al PMB <4% 5 cm thick; 20% f g ; 1.45 mm skin; 19

20 Results: Skin shielding models Monoenergetic Beam 1% f g 100% f g 20

21 Results: Skin shielding models Monoenergetic Beam Depth Dose 18 kev 20% f g 2 cm breast 8 cm breast 21

22 Results: Skin shielding models Polyenergetic Beam 2 cm 8 cm 20% f g 15% 16% 36% 34% 22

23 Results: Skin shielding models Polyenergetic Beam Mo/Mo 28 kv 2 cm breast 21% 23% 23

24 Results: Skin shielding models Polyenergetic Beam Mo/Mo 28 kv 21% 1% f g 17% 24

25 Results: Summary Polyenergetic Beam Skin Models 25

26 Outline Motivation Methodology Results Mammography Dosimetry Mean Glandular Dose Implemented Models How? MGD vs Skin Model Differences Conclusions Summary 26

27 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 28 Acknowledgement Process 2016/ Process 2015/ Process / Lab Members and Alumni Collaborators Rodrigo T. Massera Bruno L. Rodrigues José Maria Fernandez-Varea

29 Our Institution Funded in 1966 Credits: Lucas Rodolfo de Castro Moura University of Campinas (UNICAMP): 1st in Latin America

30 Thank You! Rodrigo T. Massera MSc Student IFGW - UNICAMP 30

Patient Dosimetry in Mammography and Tomosynthesis:

2013 ICTP/IAEA Training Course on Radiation Protection of Patients Trieste Patient Dosimetry in Mammography and Tomosynthesis: What to measure, why and how John M. Boone, Ph.D., FAAPM, FSBI, FACR Professor