Evaluation of Normalized Glandular Dose Coefficients in Mammography - - PowerPoint PPT Presentation

Breast Model Validation for Monte Carlo Evaluation of Normalized Glandular Dose Coefficients in Mammography

• A. Sarno, G. Mettivier, F. Di Lillo, K. Bliznakova, I. Sechopoulos and P. Russo

Napoli, 17th October 2017

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

sarno@na.infn.it

Dosimetry in mammography

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Mean Glandular Dose (MGD) = DgN ( or c·g·s) · K

Air kerma at the breast surface Coefficients calculated via MC simulations

Breast model assumptions: skin thickness

3 Model from Skin layer (mm) Adipose layer (mm) Dance (1990) 0.00 5.00 Wu et al (1991) 4.00 0.00 BCT experiments 1.45 0.00 Histology 1.45 2.00

Breast model assumptions: glandular distribution

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𝑄𝑠𝑝𝑐𝑏𝑐𝑗𝑚𝑗𝑢𝑧 𝑝𝑔 𝑒𝑝𝑡𝑓 𝑏𝑐𝑡𝑝𝑠𝑐𝑢𝑗𝑝𝑜 𝑗𝑜 𝑢ℎ𝑓 𝑕𝑚𝑏𝑜𝑒 = 𝑔

g × μen

ρ 𝐹 g 𝑔

g × μen

ρ 𝐹 g + (1 − 𝑔

g) × μen

ρ 𝐹 a

MC code for breast dosimetry

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Code based on GEANT4 toolkit Physics list: Option4 Code validated vs AAPM TG195 data

16.8 keV 30 kVp 1.4 1.5 1.6 1.7

MGD per photon (mGy) This work TG-195

x10

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20% glandular breast 5-cm thick

20 voxelized patient specific breast phantoms from 3D breast images

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Mean StdDev Min Max Glandular fraction (%) 23.1 15.3 5.0 54.3 Compressed thickness (cm) 5.9 1.5 2.9 7.8

*Sechopoulos et al 2012, "Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry." Med. Phys. 39 5050-5059.

MC validation for the heterogeneous model

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10 20 30 40 50 60 70 80 2 4 6 8 10 12 Breast thickness = 5 cm 20% glandular 100*(MGDhomo - MGDhete)/MGDhomo Incident photon energy, E (keV) Homogeneous vs. heterogeneous breast model

Skin thickness influence on the MGD

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10 20 30 40 25 50 75 100 100*(MGD1.45 - MGDx)/MGD1.45 Incident photon energy, E (keV) Skin thickness:

5-mm 4-mm 3-mm 2-mm Ref.: 1.45 mm skin thickenss

Compressed breast thickness = 5 cm; glandular fraction = 20%

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10 20 30 40

• 100
• 80
• 60
• 40
• 20

100*(MGDD-MGD1.45)/MGDD Incident photon energy, E (keV) 1.45 mm skin layer vs. 5 mm adipose

Skin model influence on the MGD

Compressed breast thickness = 5 cm; glandular fraction = 20%

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Standard models vs. patient specific phantoms

D a n c e m

• d

e l W u e t a l m

• d

e l 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

Mean = 0.89

Median

Mean = 1.01

75th percentile 25th percentile 10th percentile Min 90th percentile

Model - to - patien specific MGD

Max

MGD ratio

W/Al 0.7 mm kVp tuned on the breast thickness

1 . 4 5 m m s k i n 1 . 4 5 m m s k i n + 2 m m f a t 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

W/Al 0.7 mm kVp tuned on the breast thickness

MGD ratio

Model - to - patien specific MGD

Mean = 1.01 Mean = 0.98

Max 90th percentile 75th percentile Median 25th percentile 10th percentile Min

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New models vs. patient specific phantoms

• The skin model in MC simulations presents a large influence on MGD

estimates;

• A simple breast model can produce MGD underestimation up to about

40% when compared to the dose estimates via patient specific breast phantoms;

• The model proposed by Wu et al (1991) led to the lowest dose
• verestimation (18%) combined with the highest MGD underestimation

(-40%) for a specific breast;

• Breast model with a 1.45 mm skin thickness and the Dance’s model led to

the lowest differences (1%), on average, when compared to patient specific breast phantoms, with respect to Wu’s model (-11%).

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Conclusions

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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