Monte Carlo evaluation of glandular dose estimates in X-ray breast - - PowerPoint PPT Presentation

Monte Carlo evaluation of glandular dose estimates in X-ray breast computed tomography

• G. Mettivier, K. Bliznakova, A. Sarno, F. Di Lillo, J.M. Boone and P. Russo

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sarno@na.infn.it

International Conference on Monte Carlo Techniques for Medical Application (MCMA2017) - Napoli 15th-18th October 2017

Napoli, 18th October 2017

Computed tomography dedicated to the breast

• Fully 3D images
• Uncompressed breast
• 49-80 kVp W spectra

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• J. M. Boone et al. Dedicated Breast CT: Radiation Dose and

Image Quality Evaluation1. Radiology 221(3), 2001

Dosimetric parameters in breast CT

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MGD = DgNCT × K

Normalized glandular dose coefficient in CT calculated via MC simulations Air kerma at scanner isocenter

• Boone JM et al 2004 Med. Phys.
• Thacker and Glick 2004 Phys. Med. Biol.
• Sechopoulos et al 2010 Med. Phys.

Breast CT scanner at UC Davis

Breast model and irradiation geometry

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• Cylindrical breast
• Breast height = 1, 1.5, 2*breast radius
• Homogeneous adipose/glandular mix
• Skin thickness = 1.45 mm
• Chest-to-central beam = 0 cm

Skin thickness influence on MGD

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10 20 30 40 50 60 0.2 0.4 0.6 0.8 1.0 DgNCT deviation (unitary) Incident photon energy (keV)

2 mm 3 mm 4 mm to 1.45 mm skin thickness Breast diameter = 14 cm Glandular fraction = 20%

Monoenergetic and Polyenergetic DgNCT

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10 20 30 40 50 60 0.0 0.2 0.4 0.6 0.8 1.0 DgNCT (mGy/mGy) Incident photon energy (keV)

Monochromatic DgN Breast diameter = 12 cm Glandular fraction = 25%

6 8 10 12 14 16 18 0.25 0.30 0.35 0.40 0.45 0.50 0.55 pDgNCT (mGy/mGy) Breast diameter (cm)

Glandular fraction: 0% 25% 50% 75% 100%

49 kVp HVL = 1.29 mm Al Polychromatic DgN

Dataset for monoenergetic DgNCT

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10 20 30 40 50 60 70 80 0.0 0.2 0.4 0.6 0.8 1.0

Calculated values 8th-order polynomlial fit-curve

DgNCT Primary photon energy (keV)

Breast diameter = 120 mm Breast glandularity = 25% Breast height= Radius x 2 Radius x 1.5 Radius x 1 Fitting R

2 > 0.9999

Patient specific breast phantoms

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Simple model vs patient specific breast phantoms

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A case study

In this specific case the MGD calculated with the homogeneous cylindrical model is 21% lower than that calculated with the patient specific phantom (49 kVp; W/Al)

DgNCT coefficients validation

10 0.8 1.0 1.2 1.4

Min Max

• Hom. cont./Real breast model

DgN

90

th percentile

10

th percentile

75

th percentile

25

th percentile

Median Mean

49 kVp HVL = 1.29 mm Al

20 segmented 3D breasts

Mean Std Min Max Glandular fraction (%) 28.0 22.6 4.9 76.0 Diameter (cm) 11.2 2.1 6.4 14.6

*results presented at ECMP 2016 by A. Sarno

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Conclusions

• A breast model for MGD evaluation in breast CT has been

presented;

• Monochromatic and polychromatic DgN coefficients have been

provided;

• The dose estimates with a simple model led to MGD differences

when compared to that evaluated with patient specific breast phantoms;

• The ongoing work for patient specific dose estimates has been

shown.

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Thank you!!! Any questions?

sarno@na.infn.it

International Conference on Monte Carlo Techniques for Medical Application (MCMA2017) - Napoli 15th-18th October 2017