Air kerma calculation in Monte Carlo simulations for deriving normalized glandular dose coefficients in mammography

Sarno, Antonio; Mettivier, Giovanni; Russo, Paolo

doi:10.1088/1361-6560/aa7016

Cited by 19 publications

(17 citation statements)

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“…The factor G was evaluated at energy E of the photon which deposits energy or, in case of the electron energy loss, at the energy of the photon which generated such an electron through a photoelectric or incoherent interaction. K was evaluated under the compression paddle, in a square region of interest ( S ) of area 0.8 × 0.8 cm 2 at the entrance breast skin surface attached to the chest wall using:

K = \sum_{i} \frac{E_{i} \times \frac{μ_{en}}{normalρ} {()(, E_{i})}_{normalair}}{S \times c o s {italicθ}_{i}}

where E i is the photon energy of the i‐th photon crossing the scoring surface, [μ en /ρ]( E i ) air is the mass energy absorption coefficient of dry air and θ i is the angle between the photon direction and the vector normal to the scoring plane. In the evaluation of K , both primary radiation and scatter from the compression paddle were taken into account, but backscatter from the breast was not included.…”

Section: Methodsmentioning

confidence: 99%

A Monte Carlo model for mean glandular dose evaluation in spot compression mammography

et al. 2017

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Purpose To characterize the dependence of normalized glandular dose (DgN) on various breast model and image acquisition parameters during spot compression mammography and other partial breast irradiation conditions, and evaluate alternative previously-proposed dose-related metrics for this breast imaging modality. Methods Using Monte Carlo simulations with both simple homogeneous breast models and patient-specific breasts, three different dose related metrics for spot compression mammography were compared: the standard DgN, the normalized glandular dose to only the directly irradiated portion of the breast (DgNv), and the DgN obtained by the product of the DgN for full field irradiation and the ratio of the mid-height area of the irradiated breast to the entire breast area (DgNM). How these metrics vary with field-of-view size, spot area thickness, x-ray energy, spot area and position, breast shape and size, and system geometry was characterized for the simple breast model and a comparison of the simple model results to those with patient-specific breasts was also performed. Results DgN in spot compression mammography can vary considerably with breast area. However, the difference in breast thickness between the spot compressed area and the uncompressed area does not introduce a variation in DgN. As long as the spot compressed area is completely within the breast area and only the compressed breast portion is directly irradiated, its position and size does not introduce a variation in DgN for the homogeneous breast model. As expected, DgN is lower than DgNv for all partial breast irradiation areas, especially when considering spot compression areas within the clinically used range. DgNM underestimates DgN by 6.7% for a W/Rh spectrum at 28 kVp and for a 9×9 cm2 compression paddle. Conclusion As part of the development of a new breast dosimetry model, a task undertaken by the American Association of Physicists in Medicine and the European Federation of Organizations of Medical Physics, these results provide insight on how DgN and two alternative dose metrics behave with various image acquisition and model parameters.

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K = \sum_{i} \frac{E_{i} \times \frac{μ_{en}}{normalρ} {()(, E_{i})}_{normalair}}{S \times c o s {italicθ}_{i}}

Section: Methodsmentioning

confidence: 99%

A Monte Carlo model for mean glandular dose evaluation in spot compression mammography

et al. 2017

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“…A MC code for MGD calculation in X-ray breast imaging was developed and presented in previous papers [19,[21][22][23][24]. It is based on GEANT4 ver.…”

Section: Codementioning

confidence: 99%

Homogeneous vs. patient specific breast models for Monte Carlo evaluation of mean glandular dose in mammography

et al. 2018

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Section: Methodsmentioning

confidence: 99%

“…To normalize the photon fluence in the MC simulation to that used in the experiments, a scale factor was used, defined as the ratio between the experimentally used air kerma (measured by the IOC) and the simulated incident air kerma (analytically evaluated in the MC code) in a square region of area 3 9 3 cm 2 placed 4 cm from the chest wall, laterally centered and under the compression paddle, as suggested by Sarno et al 34 The W/Rh spectrum at 28 kV was modeled using the TASMICS model 35 by adjusting the thickness of the modeled rhodium filter to minimize the difference between the predicted and the measured attenuation of the seven different aluminum layers previously obtained.…”

Section: F Geant4 Monte Carlo Simulationsmentioning

confidence: 99%

Internal breast dosimetry in mammography: Monte Carlo validation in homogeneous and anthropomorphic breast phantoms with a clinical mammography system

2018

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PurposeTo validate Monte Carlo (MC)‐based breast dosimetry estimations using both a homogeneous and a 3D anthropomorphic breast phantom under polyenergetic irradiation for internal breast dosimetry purposes.MethodsExperimental measurements were performed with a clinical digital mammography system (Mammomat Inspiration, Siemens Healthcare), using the x‐ray spectrum selected by the automatic exposure control and a tube current‐exposure time product of 360 mAs. A homogeneous 50% glandular breast phantom and a 3D anthropomorphic breast phantom were used to investigate the dose at different depths (range 0–4 cm with 1 cm steps) for the homogeneous case and at a depth of 2.25 cm for the anthropomorphic case. Local dose deposition was measured using thermoluminescent dosimeters (TLD), metal oxide semiconductor field‐effect transistor dosimeters (MOSFET), and GafChromic™ films. A Geant4‐based MC simulation was modified to match the clinical experimental setup. Thirty sensitive volumes (3.2 × 3.2 × 0.38 mm3) on the axial‐phantom plane were included at each depth in the simulation to characterize the internal dose variation and compare it to the experimental TLD and MOSFET measurements. The experimental 2D dose maps obtained with the GafChromic™ films were compared to the simulated 2D dose distributions.ResultsDue to the energy dependence of the dosimeters and due to x‐ray beam hardening, dosimeters based on these three technologies have to be calibrated at each depth of the phantom. As expected, the dose was found to decrease with increasing phantom depth, with the reduction being ~93% after 4 cm for the homogeneous breast phantom. The 2D dose map showed nonuniformities in the dose distribution in the axial plane of the phantom. The mean combined standard uncertainty increased with phantom depth by up to 5.3% for TLD, 6.3% for MOSFET, and 9.6% for GafChromic™ film. In the case of a heterogeneous phantom, the dosimeters are able to detect local dose gradient variations. In particular, GafChromic™ film showed local dose variations of about 46% at the boundaries of two materials.ConclusionsResults showed a good agreement between experimental measurements (with TLD and MOSFET) and MC data for both homogeneous and anthropomorphic breast phantoms. Larger discrepancies are found when comparing the GafChromic™ dose values to the MC results due to the inherent less precise nature of the former.MC validations in a heterogeneous background at the level of local dose deposition and in absolute terms play a fundamental role in the development of an accurate method to estimate radiation dose. The potential introduction of a breast dosimetry model involving a nonhomogeneous glandular/adipose tissue composition makes the validation of internal dose distributions estimates crucial.

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Air kerma calculation in Monte Carlo simulations for deriving normalized glandular dose coefficients in mammography

Cited by 19 publications

References 18 publications

A Monte Carlo model for mean glandular dose evaluation in spot compression mammography

A Monte Carlo model for mean glandular dose evaluation in spot compression mammography

Homogeneous vs. patient specific breast models for Monte Carlo evaluation of mean glandular dose in mammography

Internal breast dosimetry in mammography: Monte Carlo validation in homogeneous and anthropomorphic breast phantoms with a clinical mammography system

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