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Average glandular dose coefficients for pendant‐geometry breast CT using realistic breast phantoms
Author(s) -
Hernandez Andrew M.,
Boone John M.
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12477
Subject(s) - imaging phantom , monte carlo method , nuclear medicine , radius , dosimetry , physics , breast imaging , cylinder , materials science , geometry , optics , mammography , mathematics , breast cancer , medicine , statistics , computer science , computer security , cancer
Purpose To design volume‐specific breast phantoms from breast CT ( bCT ) data sets and estimate the associated normalized mean glandular dose coefficients for breast CT using Monte Carlo methods. Methods A large cohort of bCT data sets (N = 215) was used to evaluate breast volume into quintiles (plus the top 5%). The average radius profile was then determined for each of the six volume‐specific groups and used to both fabricate physical phantoms and generate mathematical phantoms (V1‐V6; “V” denotes classification by volume). The MCNP 6 Monte Carlo code was used to model a prototype bCT system fabricated at our institution; and this model was validated against physical measurements in the fabricated phantoms. The mathematical phantoms were used to simulate normalized mean glandular dose coefficients for both monoenergetic source photons “Dg N CT (E)” (8–70 keV in 1 keV intervals) and polyenergetic x‐ray beams “ pDgN CT ” (35–70 kV in 1 kV intervals). The Monte Carlo code was used to study the influence of breast size (V1 vs. V5) and glandular fraction (6.4% vs. 45.8%) on glandular dose. The pDgN CT coefficients estimated for the V1, V3, and V5 phantoms were also compared to those generated using simple, cylindrical phantoms with equivalent volume and two geometrical constraints including; (a) cylinder radius determined at the breast phantom chest wall “R cw ”; and (b) cylinder radius determined at the breast phantom center‐of‐mass “R COM ”. Results Satisfactory agreement was observed for dose estimations using MCNP 6 compared with both physical measurements in the V1, V3, and V5 phantoms (R 2 = 0.995) and reference bCT dose coefficients using simple phantoms (R 2 = 0.999). For a 49 kV spectrum with 1.5 mm Al filtration, differences in glandular fraction [6.5% (5th percentile) vs. 45.8% (95th percentile)] had a 13.2% influence on pDgN CT for the V3 phantom, and differences in breast size (V1 vs. V5) had a 16.6% influence on pDgN CT for a breast composed of 17% (median) fibroglandular tissue. For cylindrical phantoms with a radius of R COM , the differences were 1.5%, 0.1%, and 2.1% compared with the V1, V3, and V5 phantoms, respectively. Conclusion Breast phantoms were designed using a large cohort of bCT data sets across a range of six breast sizes. These phantoms were then fabricated and used for the estimation of glandular dose in breast CT . The mathematical phantoms and associated glandular dose coefficients for a range of breast sizes (V1–V6) and glandular fractions (5th to 95th percentiles) are available for interested users.