Image quality and dose assessment in digital breast tomosynthesis: A Monte Carlo study

Radiation dose from digital breast tomosynthesis screening - A comparison with full field digital mammography

OBJECTIVES

To compare Mean Glandular Dose (MGD) and effective dose from digital breast tomosynthesis (DBT) screening with that from full field digital mammography (FFDM) screening.

METHOD

To simulate compressed breasts, two Perspex-polyethylene breast phantoms were used, one phantom for compressed breast in craniocaudal and the other for compressed breast in mediolateral oblique. An adult ATOM dosimetry phantom was loaded with high sensitivity thermoluminescence dosimeters; the phantom was then positioned on Hologic Selenia Dimensions mammographic machine to imitate DBT and 4-view FFDM screening. Organ radiation doses were measured from 4-view DBT and 4-view FFDM (craniocaudal and mediolateral oblique views for each breast). Organ radiation doses were used to calculate effective dose from one screening session.

RESULTS

MGD for DBT was 3.6 mGy; MGD for FFDM was 2.8 mGy. For DBT, other organs (e.g. thymus, lungs, salivary glands, thyroid, contralateral breast and bone marrow) radiation dose was also higher than for FFDM. The use of DBT for breast cancer screening increases the effective dose (E) of one screening session by 22%. E for DBT was 0.44 mSv; E for FFDM was 0.34 mSv.

CONCLUSION

The use of DBT for breast cancer screening increases the radiation dose to screening clients.

A Brief Review on Breast Carcinoma and Deliberation on Current Non Invasive Imaging Techniques for Detection

BACKGROUND

Breast carcinoma is a life threatening disease that accounts for 25.1% of all carcinoma among women worldwide. Early detection of the disease enhances the chance for survival.

DISCUSSION

This paper presents comprehensive report on breast carcinoma disease and its modalities available for detection and diagnosis, as it delves into the screening and detection modalities with special focus placed on the non-invasive techniques and its recent advancement work done, as well as a proposal on a novel method for the application of early breast carcinoma detection.

CONCLUSION

This paper aims to serve as a foundation guidance for the reader to attain bird's eye understanding on breast carcinoma disease and its current non-invasive modalities.

Interest of systematic tomosynthesis (3D mammography) with synthetic 2D mammography in breast cancer screening

Full field digital mammography (FFDM) is the current pillar of breast cancer screening program. However, the emerging technique digital breast tomosynthesis (DBT) has demonstrated a significant increase in the sensibility of cancer detection in several large cohort trials. DBT is particularly helpful for young patients, dense breasts and soft masses due to its ability to reduce overlapping of tissue. In such a population of women, radiologists are more confident and the recall rates are reduced together with a higher positive predictive value. To reduce the breast absorbed doses of screened women and facilitate the workflow, a synthetized two-dimensional (2D) digital mammography (sDM) is obtained from DBT to replace the FFDM. No significant differences regarding detection of anomalies have been reported with respect to FFDM. These results validate a modern strategy for breast cancer screening supported by two views of DBT with sDM. In terms of mean absorbed doses, this strategy is around 1.5 mGy/view and almost equivalent to FFDM. In Europe, major limitations to such evolution are public health policies especially agreements and reimbursement for the technique being used in organized screening.

Assessment of Mean Glandular Dose in Mammography System with Different Anode-Filter Combinations Using MCNP Code

Background

X-ray mammography is one of the general methods for early detection of breast cancer. Since glandular tissue in the breast is sensitive to radiation and it increases the risk of cancer, the given dose to the patient is very important in mammography.

Objectives

The aim of this study was to determine the average absorbed dose of X-ray radiation in the glandular tissue of the breast during mammography examinations as well as investigating factors that influence the mean glandular dose (MGD). One of the precise methods for determination of MGD absorbed by the breast is Monte Carlo simulation method which is widely used to assess the dose.

Materials and Methods

We studied some different X-ray sources and exposure factors that affect the MGD. “Midi-future” digital mammography system with amorphous-selenium detector was simulated using the Monte Carlo N-particle extended (MCNPX) code. Different anode/filter combinations such as tungsten/silver (W/Ag), tungsten/rhodium (W/Rh), and rhodium/aluminium (Rh/Al) were simulated in this study. The voltage of X-ray tube ranged from 24 kV to 32 kV with 2 kV intervals and the breast phantom thickness ranged from 3 to 8 cm, and glandular fraction g varied from 10% to 100%.

Results

MGD was measured for different anode/filter combinations and the effects of changing tube voltage, phantom thickness, combination and glandular breast tissue on MGD were studied. As glandular g and X-ray tube voltage increased, the breast dose increased too, and the increase of breast phantom thickness led to the decrease of MGD. The obtained results for MGD were consistent with the result of Boone et al. that was previously reported.

Conclusion

By comparing the results, we saw that W/Rh anode/filter combination is the best choice in breast mammography imaging because of the lowest delivered dose in comparison with W/Ag and Rh/Al. Moreover, breast thickness and g value have significant effects on MGD.

Monte-Carlo simulation of a slot-scanning digital mammography system for tomosynthesis

BACKGROUND

Digital breast tomosynthesis (DBT) reconstructs planar slices of the breast based on two-dimensional angular projections. Early studies and clinical trials show that DBT is an improvement over full field digital mammography (FFDM) because it provides the radiologist with better image quality and more information.

OBJECTIVE

This paper presents a simulation system to model the performance of a slot-scanning FFDM and DBT system.

METHODS

A tissue-equivalent three dimensional (3D) breast phantom was constructed, validated for slot-scanning digital mammography and used in simulating digital breast tomosynthesis. The simulation system was validated by comparing images acquired with a slot-scanning mammography machine with simulated phantom images, using the edge-test method and image quality metrics modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE). Different two-dimensional (2D) projections of the 3D phantom were simulated and the phantom was reconstructed using filtered backprojection.

RESULTS

Image quality metrics showed equivalence between simulated and real images.

CONCLUSIONS

The simulation tool is suitable for slot-scanning FFDM and DBT and may be used for the design and comparison of mammography systems.

Determination of backscatter factors in breast tomosynthesis using MCNPX simulations and measurements

The perspective of adding digital breast tomosynthesis (DBT) to standard mammography in screening raises concerns regarding the dose absorbed by the fibroglandular breast tissue. Thus, it is important to estimate accurately the mean glandular dose (MGD), although there are no standard protocols for dosimetry, concerning DBT. This study aims at introducing backscatter factors (BSF) to calculate the entrance surface air kerma (ESAK), directly on patients or phantoms, in order to be introduced in the formalism proposed by Dance et al. MCNPX simulations were performed, to mimic a DBT acquisition, for a wide range of X-ray spectra. A homogeneous breast phantom with 50 % of glandular tissue was considered and several thicknesses were evaluated. Dose measurements were performed, to validate and support the simulation results. The BSF may indicate a real MGD estimation in vivo for DBT examinations and contribute for the improvement of the current guidelines used in these applications.

Effect of the glandular composition on digital breast tomosynthesis image quality and dose optimisation

In the image quality assessment for digital breast tomosynthesis (DBT), a breast phantom with an average percentage of 50 % glandular tissue is seldom used, which may not be representative of the breast tissue composition of the women undergoing such examination. This work aims at studying the effect of the glandular composition of the breast on the image quality taking into consideration different sizes of lesions. Monte Carlo simulations were performed using the state-of-the-art computer program PENELOPE to validate the image acquisition system of the DBT equipment as well as to calculate the mean glandular dose for each projection image and for different breast compositions. The integrated PENELOPE imaging tool (PenEasy) was used to calculate, in mammography, for each clinical detection task the X-ray energy that maximises the figure of merit. All the 2D cranial-caudal projections for DBT were simulated and then underwent the reconstruction process applying the Simultaneous Algebraic Reconstruction Technique. Finally, through signal-to-noise ratio analysis, the image quality in DBT was assessed.