Average absorbed breast dose (2ABD): an easy radiation dose index for digital breast tomosynthesis

Background: To propose a practical and simple method to individually evaluate the average absorbed dose for digital breast tomosynthesis. Methods: The method is based on the estimate of incident air kerma (ka,i) on the breast surface. An analytical model was developed to calculate the ka,i from the tube voltage, tube load, breast thickness, x-ray tube yield, and anode-filter combination. A homogeneous phantom was employed to simulate the breast in experimental measurements and to assess the dose-depth relationship. The ka,i values were employed to calculate the “average absorbed breast dose” (2ABD) index. Four mammographic units were used to develop and test our method under many conditions close to clinical settings. The average glandular dose (AGD) calculated following the method described by Dance et al., and the 2ABD computed through our method (i.e., from the exposure parameters) were compared in a number of conditions. Results: A good agreement was obtained between the ka,i computed through our model and that measured under different clinical conditions: discrepancies < 6% were found in all conditions. 2ABD matches with a good accuracy the AGD for a 100% glandular-breast: the minimum, maximum, and mean differences were < 0.1%, 7%, and 2.4%, respectively; the discrepancies increase with decreasing breast glandularity. Conclusions: The proposed model, based on only few exposure parameters, represents a simple way to individually calculate an index, 2ABD, which can be interpreted as the average absorbed dose in a homogeneous phantom, approximating a 100% glandular breast. The method could be easily implemented in any mammographic device performing DBT

Image Quality Comparison between Digital and Synthetic 2D Mammograms: A Qualitative and Quantitative Phantom Study

The recent introduction of digital breast tomosynthesis (DBT) have lead to improvements in sensitivity and specificity of breast cancer detection, especially in cases of tumors developed in dense breasts. Since DBT provides tomographic slices of an entire tissue volume, it reduces the inherent tissue overlapping limitation of digital mammography (DM). In addition, DBT combined with DM has been proven to decrease recall and increase invasive cancer detection rates in breast cancer screening. However, the employment of DBT+DM implies a not negligible increment of patients absorbed dose. Therefore, Synthesized mammograms (SMs) generated from the DBT data have been recently introduced to eliminate the need of an additional DM. However, several studies showed differences between DM and SM images and some studies found contrasting results in terms of image quality when DM and SM images were compared. In our phantom study, we objectively compare image quality of SM and DM images in terms of noise, spatial resolution and contrast properties. Additionally, a qualitative analysis of the ACR mammographic phantom was performed in both modalities to assess the detectability of different features. SM images were characterized by different texture with respect to DM images, showing lower overall performances in terms of contrast-to-noise ratio and modulation transfer function. However, the goal of SM images is to provide a useful two-dimensional guide complementary to the DBT dataset and the performances in terms of high-contrast features detectability were satisfactory in comparison to those obtained in DM

Image quality in synthetic mammograms obtained from 15◦ and 40◦ digital breast tomosynthesis: a preliminary comparative phantom study.

The aim of this phantom study was to perform an image quality comparison between synthe- sized mammograms reconstructed from digital breast tomosynthesis acquisitions with 15◦ (SM15) and 40◦ (SM40) X-ray tube angular range in a commercial system. In order to investigate the spatial resolution, contrast and noise properties of the images, the Modu- lation Transfer Function (MTF), the image contrast, the Signal-to-Noise Ratio (SNR) and the Contrast-Detail (CD) curves were evaluated. Our results showed that SM40 images expressed higher MTF than SM15, but similar contrast values and lower SNR levels. Addi- tionally, lower CD performances were found for SM40 with respect to SM15

Comprehensive assessment of image quality in synthetic and digital mammography: a quantitative comparison

Recent advances in digital breast tomosynthesis (DBT) technology were focused on the reconstruction of 2D “Synthesized Mammograms” (SMs) from DBT dataset. The introduction of SMs could avoid an additional digital mammography (DM) which is often required in complement to DBT examinations. Therefore, breast absorbed dose and compression time can be significantly reduced in DBT+SM procedures with respect to DBT+DM modality. However, to date, a limited number of studies have objectively characterised the image quality of SMs with respect to DM images. Therefore, the aim of this phantom study was to comprehensively compare SMs and DM images in terms of several image quality parameters. A Selenia Dimensions system (Hologic, Bedford, Mass, USA) was employed in this work. Five different phantoms were adopted to study noise, contrast and spatial resolution properties of the images. Specifically, noise power spectrum (NPS), maps of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), modulation transfer function (MTF) and contrast-detail (CD) thresholds were evaluated both for SM and DM modalities. SMs were characterised by different texture, noise and SNR spatial distribution properties with respect to DM images. Additionally, while in some conditions SM provides higher CNR than DM, lower overall performances in terms spatial resolution and CD curves were found in comparison to DM images. Therefore, given the great benefits of SMs in terms of dose and compression time saving, further clinical investigations on SMs image quality properties could be of practical interest to integrate our findings

Monte carlo methods for assessment of the mean glandular dose in mammography: Simulations in homogeneous phantoms

The rationale of this study is to perform a personalized dosimetry in digital mammography, using Monte Carlo simulations. We developed a GEANT4-based application that reproduces mammographic investigations editable in different setups and conditions. Mean Glandular Dose (MGD) is estimated for different compressed breast sizes and compositions. Breast compositions are obtained with homogeneous mixture of glandular and adipose tissues. The simulated setup reproduces the Hologic Selenia ® Dimensions ® Mammography System and the TASMIPM tool for deriving the photon fluence from the X-ray source has been employed. The influence of different skin models is also investigated, deriving the mean glandular dose in the breast using adipose tissue for different skin thicknesses, from 2 mm to 5 mm, and a dedicated composition found in literature with the specific thickness of 1.45 mm. We denoted different photon shielding properties on the MGD values

Image quality comparison between digital and synthetic 2D mammograms: A qualitative and quantitative phantom study

The recent introduction of digital breast tomosynthesis (DBT) have lead to improvements in sensitivity and specificity of breast cancer detection, especially in cases of tumors developed in dense breasts. Since DBT provides tomographic slices of an entire tissue volume, it reduces the inherent tissue overlapping limitation of digital mammography (DM). In addition, DBT combined with DM has been proven to decrease recall and increase invasive cancer detection rates in breast cancer screening. However, the employment of DBT+DM implies a not negligible increment of patients absorbed dose. Therefore, Synthesized mammograms (SMs) generated from the DBT data have been recently introduced to eliminate the need of an additional DM. However, several studies showed differences between DM and SM images and some studies found contrasting results in terms of image quality when DM and SM images were compared. In our phantom study, we objectively compare image quality of SM and DM images in terms of noise, spatial resolution and contrast properties. Additionally, a qualitative analysis of the ACR mammographic phantom was performed in both modalities to assess the detectability of different features. SM images were characterized by different texture with respect to DM images, showing lower overall performances in terms of contrast-to-noise ratio and modulation transfer function. However, the goal of SM images is to provide a useful two-dimensional guide complementary to the DBT dataset and the performances in terms of high-contrast features detectability were satisfactory in comparison to those obtained in DM

Normalized glandular dose coefficients for digital breast tomosynthesis systems with a homogeneous breast model

This work aims at calculating and releasing tabulated values of dose conversion coefficients, DgNDBT, for mean glandular dose (MGD) estimates in digital breast tomosynthesis (DBT). The DgNDBT coefficients are proposed as unique conversion coefficients for MGD estimates, in place of dose conversion coefficients in mammography (DgNDM or c, g, s triad as proposed in worldwide quality assurance protocols) used together with the T correction factor. DgNDBT is the MGD per unit incident air kerma measured at the breast surface for a 0° projection and the entire tube load used for the scan. The dataset of polyenergetic DgNDBT coefficients was derived via a Monte Carlo software based on the Geant4 toolkit. Dose coefficients were calculated for a grid of values of breast characteristics (breast thickness in the range 20-90 mm and glandular fraction by mass of 1%, 25%, 50%, 75%, 100%) and the simulated geometries, scan protocols, irradiation geometries and typical spectral qualities replicated those of six commercial DBT systems (GE SenoClaire, Hologic Selenia Dimensions, GE Senographe Pristina, Fujifilm Amulet Innovality, Siemens Mammomat Inspiration and IMS Giotto Class). For given breast characteristics, target/filter combination, tube voltage and half value layer (HVL), two spectra with two HVL values have been simulated in order to permit MGD estimates from experimental HVL values via mathematical interpolation from tabulated values. The adopted breast model assumes homogenous composition of glandular and adipose tissues; it includes a 1.45 mm thick skin envelope in place of the 4-5 mm envelope commonly adopted in dosimetry protocols. The simulation code was validated versus AAPM Task group 195 Monte Carlo reference data sets (absolute differences not higher than 1.1%) and by comparison to relative dosimetry measurements with radiochromic film in a PMMA test object (differences within the maximum experimental uncertainty of 11%). The calculated coefficients show maximum relative deviations of -17.6% and +6.1% from those provided by the DBT dose coefficients adopted in the EUREF protocol and of 1.5%, on average, from data in the AAPM TG223 report. A spreadsheet is provided for interpolating the tabulated DgNDBT coefficients for arbitrary values of HVL, compressed breast thickness and glandular fraction, in the corresponding investigated ranges, for each DBT unit modeled in this work

Monte Carlo simulations for X-ray breast dosimetry using homogeneous and heterogeneous phantoms

In this work a proposal for a new heterogeneous breast phantom to be adopted in Monte Carlo calculations for dosimetry in digital mammography is presented. The heterogeneous phantom is designed to avoid the current assumption of the homogeneous compound of the breast tissue adopted in the current international dosimetry protocols. With the aim to improve Monte Carlo accuracy, the phantom is chosen between two models developed using different approaches: a voxelized phantom and a ducts-and-lobules phantom using mathematical solids. For both models, dose estimates are calculated and compared with the reference homogeneous phantom, and the most reliable digital phantom is chosen and proposed for dosimetry purpose

Monte Carlo simulations for X-ray breast dosimetry using homogeneous and heterogeneous phantoms

In this work a proposal for a new heterogeneous breast phantom to be adopted in Monte Carlo calculations for dosimetry in digital mammography is presented. The heterogeneous phantom is designed to avoid the current assumption of the homogeneous compound of the breast tissue adopted in the current international dosimetry protocols. With the aim to improve Monte Carlo accuracy, the phantom is chosen between two models developed using different approaches: A voxelized phantom and a ducts-and-lobules phantom using mathematical solids. For both models, dose estimates are calculated and compared with the reference homogeneous phantom, and the most reliable digital phantom is chosen and proposed for dosimetry purposes

Monte Carlo simulations for X-ray breast dosimetry using homogeneous and heterogeneous phantoms.

Monte Carlo simulations are used to provide an estimate of the Mean Glandular Dose (MGD) for X-ray Digital Mammography and Digital Breast Tomosynthesis, where digital breast phantoms made by a homogeneous mixture of adipose and glandular tissues are involved for X-ray dosimetry. Nevertheless, studies in the literature suggest an overestimate of the MGD, since the gland is not distributed evenly in the breast volume. In this work a GEANT4- based Monte Carlo code has been developed for creating heterogeneous breast phantoms for dosimetry, which involve geometrical shapes forming the gland tree. The breast models are then used to compute the MGD estimates