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A Monte Carlo simulation toolkit for optimization studies of digital mammography. Sakellaris T 1* , Pascoal A 1 and Koutalonis M 2. 1 Faculty of Engineering, Catholic University of Portugal, Lisbon, Portugal 2 Bart's Health NHS Trust, Clinical Physics Department, London, United Kingdom. - PowerPoint PPT Presentation
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The user selects which components to irradiate e.g. edge and/or breast phantom
and/or grid and detector
A Monte Carlo simulation toolkit for optimization studies of digital mammography
Sakellaris T1*, Pascoal A1 and Koutalonis M2 1Faculty of Engineering, Catholic University of Portugal, Lisbon, Portugal
2Bart's Health NHS Trust, Clinical Physics Department, London, United Kingdom
1. PURPOSEDevelopment of a Monte Carlo simulation toolkit dedicated to the design of optimization studies of digital mammography.
2. METHODA validated Monte Carlo model for conventional mammography[1], which considers a mathematical breast phantom with various types and shapes of clinical relevant lesions (microcalcifications and masses), was extended to include an a-Se detector, a linear parallel anti-scatter grid (stationary and moving) as well as a partially isocentric moving focal spot for oblique irradiations. A validated Monte Carlo dose calculation algorithm was integrated in the model to enable 3-D glandular dose estimations[2]. The code is currently being associated with a graphical user interface (GUI). The detector model simulates x ray-matter interactions, and produces images considering the energy absorbed inside a-Se and Poisson noise. Its validation was made comparing the simulation pre-sampling MTF (MTFpre) with theory[3]. The grid simulation is based on a compartmental approach of photon transport and was validated comparing the signal difference to noise ratio improvement factor (SIF) with published data[4]. The simulation of oblique irradiation uses Euler transformations and it was validated comparing the simulation MTF due to oblique x-ray incidence (MTFobl) with theoretical predictions[5].3. VALIDATION RESULTSThe MTFpre as well as MTFobl differed approximately by 1.2% (< 0.5 lp/mm) from theoretical, and the SIF factor differed 4.7% from the published values. 4. THE SIMULATION TOOLKIT
Varying Focus-Breast Distance (Magnification
mammography)
Focal spot: Point or With finite dimensions and 3 intensity distributions:
Gaussian Distribution
Double Edge Distribution
Uniform Distribution
Linear anti-scatter grid: Stationary or Moving User defined:• Strip material, thickness and
height• Interspace material and width
a-Se digital detector: User defined:• Detector dimensions• Number of pixels• Detector thickness
Collimator
Overview of simulation capabilities
X-ray energies: Mammographic spectra
(From tabulated data) or
Monoenergetic spectra Mathematical breast phantom: Semi-cylindrical slice Varying radius, thickness & composition Homogeneous or With various types & shapes of clinical
relevant lesions (microcalcifications & masses) and/or
Test-object patterns (e.g. bar patterns)
Glandular & Adipose dose calculations 3-D dose distributions User defines voxel size
Edge-test device (tiltable): Parallel or Vertical to chest wall User defined:• Focus-edge distance• Edge dimensions, material,
thickness and angle
Moving Focal spot Partial isocentric motion User defined focus-center of
rotation (COR) distance and irradiation angle
Compressor paddle
6. REFERENCES
7. ACKNOWLEDGEMENTS
[1] Spyrou G, Panayiotakis G and Tzanakos G 2000 MASTOS: Mammography Simulation Tool for design Optimization Studies Med. Inform. 25 275-93[2] Delis H, Spyrou G, Panayiotakis G and Tzanakos G 2005a DOSIS: a Monte Carlo simulation program for dose related studies in mammography Eur. J. Radiol. 54 371–6[3] Zhao W, Ji W G and Rowlands J A 2001 Effects of characteristic x rays on the noise power spectra and detective quantum efficiency of photoconductive x-ray detectors
Med. Phys. 28 2039-49[4] Cunha D M, Tomal A and Poletti M E 2010 Evaluation of scatter-to-primary ratio, grid performance and normalized average glandular dose in mammography by Monte
Carlo simulation including interference and energy broadening effects Phys. Med. Biol. 55 4335-59[5] Que W and Rowlands J A 1995 X-ray imaging using amorphous selenium: inherent spatial resolution Med. Phys. 22 365-74
5. CONCLUSIONThe validated model, associated with a GUI, could provide a user-friendly simulation toolkit for multi-parametric image and dose optimization studies of digital mammography, with perspectives of its use in digital breast tomosynthesis.
We would like to thank Prof. George Spyrou for his valuable contribution in this work. This work was supported by national funding through the Foundation for Science and Technology (FCT) of Portugal within the framework of the project with reference number: PTDC/SAU-BEB/100745/2008.
Form for breast phantom design Form which summarizes the irradiation conditions
Characteristic simulation output Simulation images of a designed breast phantom
Image from Primary & Scattered radiation Image from Scattered radiation only
Simulation images showing the effects of a moving anti-scatter gridImages from Primary & Scattered radiation
No anti-scatter grid With anti-scatter gridImages from Scattered radiation only
No anti-scatter grid With anti-scatter grid
AirCalcium Oxalate
Calcium Oxide
Simulation images of oblique irradiations with a 2 x 2 cm2 field size
0o-10o-30o +10o +30o
0o-10o-30o +10o +30o
Images from Primary & Scattered radiation
Images from Scattered radiation only
Simulation image of an edge-object placed on top of a breast phantom of 4 cm
thickness and 50% glandularity
Chest Wall side
Edge-object (Tungsten)
20 keV x-rays, 2 x 2 cm2 irradiation field, 2 cm thick breast with 50% glandularity
20 keV x-rays, 2 cm thick breast with a 2 cm radius & 50% glandularity
20 keV x-rays, 2 x 2 cm2 irradiation field, 2 cm thick breast with 50% glandularity
B r e a s t R a d i u s ( c m )
B r e a
s t T
h i c
k n e s
s ( c
m )
-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0 0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
2-D AGD distribution inside a 2 cm thick breast of 50% glandularity, irradiated with 20 keV x-rays
at 30o angle, with a field size of 2 x 2 cm2
Glandular dose (mGy)
Final Report
* Corresponding author: [email protected]
Voxel size: 100 um
The Graphical User Interface (samples) Form for digital detector specification
The code produces linearizable simulation images which can be calibrated using the Signal Transfer Property of a real a-Se system
It gives the ability to the user to calculate objective image quality metrics such as pre-sampling MTF, NNPS and DQE
It gives the ability to the user to perform complex simulations in order to calculate more specialized objective image quality metrics such as generalized (G) GMTF, GNNPS and GDQE or effective DQE
The Graphical User Interface (samples)