Estimation Of Mean Glandular Dose Research Articles

An approach to dual-energy contrast-enhanced spectral mammography (DE-CESM) using a double layer filter: dosimetric and image quality assessment

Dual-energy contrast-enhanced spectral mammography (DE-CESM) is a recently developed advanced technique in digital mammography that uses an iodinated intravenous contrast agent to assess tumor angiogenesis. The aim of this study was to investigate the diagnostic potential of DE-CESM recombined images in terms of radiation dose and image quality. A 50% fibroglandular—50% adipose, custom-made phantom with iodine inserts of 1.0 mgI cm−3, 2.0 mgI cm−3, 4.0 mgI cm−3 was used for the estimation of mean glandular dose (MGD) and the image quality. Low-energy (LE) images were acquired with the W/Rh, W/Rh + 0.01 mm Cu and W/Rh + 0.5 mm Al while high energy images (HE) are acquired with the W/Rh, W/Rh + 0.06 mm Ba, W/Rh + 0.01 mm Cu, and W/Rh + 0.03 mm Ce anode filter combinations. The total MGD was reduced up to a maximum from 1.75 mGy to 1.45 mGy by using Rh + 0.01 mm Cu double-layer filter for both LE and HE imaging of 50 mm, standard 50% fibroglandular phantom compared to Rh single-layer filter with W target. The minimum total MGD reduction (1.69 mGy) was observed when Rh + 0.5 mm Al was used for LE and Rh + 0.06 mm Ba was used for HE exposure. The image quality was comparable with the single-layer filter. The use of W/Rh + 0.01 mm Cu or W/Rh + 0.5 mm Al as target/filter combination for LE exposure and W/Rh + 0.01 mm Cu for HE exposure can reduce the additional radiation dose delivered by DE-CESM without degrading the image quality.

Comparisons of glandular breast dose between digital mammography, tomosynthesis and breast CT based on anthropomorphic patient-derived breast phantoms

PurposeTo evaluate the bias to the mean glandular dose (MGD) estimates introduced by the homogeneous breast models in digital breast tomosynthesis (DBT) and to have an insight into the glandular dose distributions in 2D (digital mammography, DM) and 3D (DBT and breast dedicated CT, BCT) x-ray breast imaging by employing breast models with realistic glandular tissue distribution and organ silhouette. MethodsA Monte Carlo software for DM, DBT and BCT simulations was adopted for the evaluation of glandular dose distribution in 60 computational anthropomorphic phantoms. These computational phantoms were derived from 3D breast images acquired via a clinical BCT scanner. Resultsg·c·s·T conversion coefficients based on homogeneous breast model led to a MGD overestimate of 18% in DBT when compared to MGD estimated via anthropomorphic phantoms; this overestimate increased up to 21% for recently computed DgNDBT conversion coefficients. The standard deviation of the glandular dose distribution in BCT resulted 60% lower than in DM and 55% lower than in DBT. The glandular dose peak – evaluated as the average value over the 5% of the gland receiving the highest dose – is 2.8 times the MGD in DM, this factor reducing to 2.6 and 1.6 in DBT and BCT, respectively. ConclusionsConventional conversion coefficients for MGD estimates based on homogeneous breast models overestimate MGD by 18%, when compared to MGD estimated via anthropomorphic phantoms. The ratio between the peak glandular dose and the MGD is 2.8 in DM. This ratio is 8% and 75% higher than in DBT and BCT, respectively.

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.

Normalized glandular dose coefficients in mammography, digital breast tomosynthesis and dedicated breast CT

PurposeTo provide mean glandular dose (MGD) estimates via Monte Carlo (MC) simulations as a function of the breast models and scan parameters in mammography, digital breast tomosynthesis (DBT) and dedicated breast CT (BCT). MethodsThe MC code was based on GEANT4 toolkit. The simulated compressed breast was either a cylinder with a semi-circular section or ad hoc shaped for oblique view (MLO). In DBT we studied the influence of breast models and exam parameters on the T-factors (i.e. the conversion factor for the calculation of the MGD in DBT from that for a 0-degree projection), and in BCT we investigated the influence on the MGD estimates of the ion chamber volume used for the air kerma measurements. ResultsIn mammography, a model representative of a breast undergoing an MLO view exam did not produce substantial differences (0.4%) in MGD estimates, when compared to a conventional cranio-caudal (CC) view breast model. The beam half value layer did not present a significant influence on T-factors in DBT (<0.8%), while the skin model presented significant influence on MGD estimates (up to 3.3% at 30 degrees scan angle), increasing for larger scan angles. We derived a correction factor for taking into account the different ion chamber volume used in MGD estimates in BCT. ConclusionsA series of MC code modules for MGD estimates in 2D and 3D breast imaging have been developed in order to take into account the most recent advances in breast models.

Estimation of mean glandular dose for contrast enhanced digital mammography: factors for use with the UK, European and IAEA breast dosimetry protocols

The UK, European and IAEA protocols for breast dosimetry in mammography use tabulations of conversion factors, which relate measurements of incident air kerma to the mean glandular dose to the breast. To supplement the existing tabulations, a Monte Carlo computer program has been used to calculate conversion factors for the high-energy spectra used for contrast enhanced digital mammography. The calculations were made for the x-ray spectra from a tungsten target (tube voltage range 40–50 kV) filtered by 0.28, 0.30 and 0.32 mm of copper, and from molybdenum and rhodium targets (tube voltage range 40–49 kV), each filtered by 0.30 mm of copper. The g-factors for all of these spectra were plotted for each breast thickness as a function of half value layer (HVL) and were found to lie on smooth curves within 0.3%. These reflect the fact that the characteristic x-rays present in the spectra from molybdenum and rhodium are heavily filtered and all the spectra are essentially Bremsstrahlung. As a consequence, the s-factor previously used in the dosimetry protocols to adjust for different target/filter combinations can be taken as unity for all of the spectra considered. Tables of g-factors and c-factors are provided for breast thicknesses in the range 20–110 mm and HVLs in the range 2.4–3.6 mm of aluminium. The tables of c-factors are given for breast glandularities in the range 0.1%–100% and for typical glandularities for women in the age bands 40–49 and 50–64 attending the UK national breast screening programme.

Comparative performance of modern digital mammography systems in a large breast screening program

To compare physical measures pertaining to image quality among digital mammography systems utilized in a large breast screening program. To examine qualitatively differences in these measures and differences in clinical cancer detection rates between CR and DR among sites within that program. As part of the routine quality assurance program for screening, field measurements are made of several variables considered to correlate with the diagnostic quality of medical images including: modulation transfer function, noise equivalent quanta, d' (an index of lesion detectability) and air kerma to allow estimation of mean glandular dose. In addition, images of the mammography accreditation phantom are evaluated. It was found that overall there were marked differences between the performance measures of DR and CR mammography systems. In particular, the modulation transfer functions obtained with the DR systems were found to be higher, even for larger detector element sizes. Similarly, the noise equivalent quanta, d', and the phantom scores were higher, while the failure rates associated with low signal-to-noise ratio and high dose were lower with DR. These results were consistent with previous findings in the authors' program that the breast cancer detection rates at sites employing CR technology were, on average, 30.6% lower than those that used DR mammography. While the clinical study was not large enough to allow a statistically powered system-by-system assessment of cancer detection accuracy, the physical measures expressing spatial resolution, and signal-to-noise ratio are consistent with the published finding that sites employing CR systems had lower cancer detection rates than those using DR systems for screening mammography.

Uncertainties involved in the estimation of mean glandular dose for women in the Norwegian Breast Cancer Screening Program (NBCSP)

The aim of this study was to reflect on the estimation of the mean glandular dose for women in Norway aged 50-69 y. Estimation of mean glandular dose (MGD) has been conducted by applying the method of Dance et al. (1990, 2000, 2009). Uncertainties in the thickness of approximately ±10 mm adds uncertainties in the MGD of approximately ±10 %, and uncertainty in the glandularity of ±0 % will lead to an uncertainty in the MGD of ±4 %. However, the inherent uncertainty in the air kerma, given by the European protocol on dosimetry, will add an uncertainty of 12 %. The total uncertainty in the MGD is estimated to be ∼20 %, taking into consideration uncertainties in compressed breast thickness (±10 %), the air kerma (12 %), change in HVL by -0.05 mm (-9.0 %), uncertainty in the s-factor of ±2.1 % and changing the glandularity to an age-dependent glandularity distribution (+8.4 %).

Estimation of mean glandular dose for breast tomosynthesis: factors for use with the UK, European and IAEA breast dosimetry protocols

A formalism is proposed for the estimation of mean glandular dose for breast tomosynthesis, which is a simple extension of the UK, European and IAEA protocols for dosimetry in conventional projection mammography. The formalism introduces t-factors for the calculation of breast dose from a single projection and T-factors for a complete exposure series. Monte Carlo calculations of t-factors have been made for an imaging geometry with full-field irradiation of the breast for a wide range of x-ray spectra, breast sizes and glandularities. The t-factors show little dependence on breast glandularity and tables are provided as a function of projection angle and breast thickness, which may be used for all x-ray spectra simulated. The T-factors for this geometry depend upon the choice of projection angles and weights per projection, but various example calculations gave values in the range 0.93–1.00. T-factors are also provided for the Sectra tomosynthesis system, which employs a scanned narrow-beam imaging geometry. In this quite different configuration, the factor (denoted TS) shows an important dependence on breast thickness, varying between 0.98 and 0.76 for 20 and 110 mm thick breasts, respectively. Additional data are given to extend the current tabulations of g-, c- and s-factors used for dosimetry of conventional 2D mammography.

Estimation of mean-glandular dose from monitoring breast entrance skin air kerma using a high sensitivity metal oxide semiconductor field effect transistor (MOSFET) dosimeter system in mammography

Estimation of mean-glandular dose (MGD) has been investigated in recent years due to the potential risks of radiation-induced carcinogenesis associated with the mammographic examination for diagnostic radiology. In this study, a new technique for immediate readout of breast entrance skin air kerma (BESAK) using high sensitivity MOSFET dosimeter after mammographic projection was introduced and a formula for the prediction of tube output with exposure records was developed. A series of appropriate conversion factors was applied to the MGD determination from the BESAK. The study results showed that signal response of the high sensitivity MOSFET exhibited excellent linearity within mammographic dose ranges, and that the energy dependence was less than 3% for each anode/filter combination at the tube potentials 25–30 kV. Good agreement was observed between the BESAK and the tube exposure output measurement for breasts thicker than 30 mm. In addition, the air kerma estimated from our prediction formula provided sufficient accuracy for thinner breasts. The average MGD from 120 Asian females was 1.5 mGy, comparable to other studies. Our results suggest that the high sensitivity MOSFET dosimeter system is a good candidate for immediately readout of BESAK after mammographic procedures.

Estimation of mean glandular dose for mammography of augmentedbreasts

The standard quantity used to relate breast surface exposure to radiation riskis the mean dose received by the radiation sensitive tissue contained withinthe female breast, the mean glandular dose (MGD). At present, little is knownabout the MGD received by women with breast implants as there is no techniqueavailable to facilitate its calculation. The present work has involvedmodification of the conventional method for MGD estimation to make itapplicable to women with augmented breasts. The technique was used tocalculate MGDs for a cohort of 80 women with breast implants, which werecompared with similar data calculated for a total of 1258 non-augmented women.Little difference was found in median MGD at low compressed breast thickness.At high breast thickness, however, the MGDs received by women with augmentedbreasts were found to be considerably lower than those relating to theirnon-augmented counterparts.

Review of Dosimetric Methods for Mammography in the UK Breast Screening Programme

The two methods used to monitor dose in mammography in the UK Breast Screening Programme are reviewed. The first is the measurement of mean glandular dose to a standard breast. The second is the estimation of mean glandular dose for individual women using the X ray exposure factors. Neither method takes account of variations in breast composition and the effect of this on estimates of landular dose are reported Applying the standard breast model using PMMA resulted in substantial overestimates of breast doses for women with large compressed breast thicknesses because they tend to have low glandular content. Conversely the use of post-exposure data to estimate the MGDs in women attending sereening with large breasts resulted in underestimates of their doses unless the relatively low levels of glandularity were taken into account. Wher estimating the MGDs for breasts of different sizes, it is important that the models and methods used take account of the strong variation in breast composition with compressed thickness.

An Investigation into Variations in the Estimation of Mean Glandular Dose in Mammography

An Investigation into Variations in the Estimation of Mean Glandular Dose in Mammography

An Investigation into Variations in the Estimation of Mean Glandular Dose in Mammography

The regular assessment of breast dose is an important part of a quality control programme in mammography. It is common practice in the United Kingdom to deduce the mean glandular dose from an estimate of air kerma at the entrance surface of a standard breast phantom manufactured from Perspex (ICI, Darwin) of nominal thickness 40 mm. Factors are used to deduce the mean glandular dose from the entrance air kerma. The objectives of this study were to assess the impact of variations in technique on the assessment of mean glandular dose and the implications for comparative surveys. It was deduced that it is possible to achieve consistent dosimetry measurements, provided standard Perspex blocks are used and tube output is measured at a specific position.

Breast Absorbed Doses in Mammography: Evaluation of Experimental and Theoretical Approaches

The low photon energies used in mammography complicate the measurement of absorbed dose. For accurate dosimetry, practical detectors require correction factors. On the contrary, Monte Carlo calculations are well suited for estimation of mean glandular dose, Dg, the relevant risk indicator. Correction factors for thin solid state detectors (LiF and Li2B4O7) are discussed and Monte Carlo methods used to analyse the dependence of Dg on irradiation geometry parameters and tissue compositions. The main results are derived for 28kV tube potential (Mo anode, 0.03 mm Mo filter) commonly used in mammography screening.

Breast Absorbed Doses in Mammography: Evaluation of Experimental and Theoretical Approaches

The low photon energies used in mammography complicate the measurement of absorbed dose. For accurate dosimetry, practical detectors require correction factors. On the contrary, Monte Carlo calculations are well suited for estimation of mean glandular dose, Dg, the relevant risk indicator. Correction factors for thin solid state detectors (LiF and Li2B4O7) are discussed and Monte Carlo methods used to analyse the dependence of Dg on irradiation geometry parameters and tissue compositions. The main results are derived for 28kV tube potential (Mo anode, 0.03 mm Mo filter) commonly used in mammography screening.