Dose comparison between screen/film and full-field digital mammography

Digital breast tomosynthesis (DBT): recommendations from the Italian College of Breast Radiologists (ICBR) by the Italian Society of Medical Radiology (SIRM) and the Italian Group for Mammography Screening (GISMa)

This position paper, issued by ICBR/SIRM and GISMa, summarizes the evidence on DBT and provides recommendations for its use. In the screening setting, DBT in adjunct to digital mammography (DM) increased detection rate by 0.5-2.7‰ and decreased false positives by 0.8-3.6% compared to DM alone in observational and double-testing experimental studies. The reduction in recall rate could be less prominent in those screening programs which already have low recall rates with DM. The increase in radiation exposure associated with DM/DBT protocols has been solved by the introduction of synthetic mammograms (sDM) reconstructed from DBT datasets. Thus, whenever possible, sDM/DBT should be preferred to DM/DBT. However, before introducing DBT as a routine screening tool for average-risk women, we should wait for the results of randomized controlled trials and for a statistically significant and clinically relevant reduction in the interval cancer rate, hopefully associated with a reduction in the advanced cancer rate. Otherwise, a potential for overdiagnosis and overtreatment cannot be excluded. Studies exploring this issue are ongoing. Screening of women at intermediate risk should follow the same recommendations, with particular protocols for women with previous BC history. In high-risk women, if mammography is performed as an adjunct to MRI or in the case of MRI contraindications, sDM/DBT protocols are suggested. Evidence exists in favor of DBT usage in women with clinical symptoms/signs and asymptomatic women with screen-detected findings recalled for work-up. The possibility to perform needle biopsy or localization under DBT guidance should be offered when DBT-only findings need characterization or surgery.

RELATIONSHIP BETWEEN RADIATION DOSE AND IMAGE QUALITY IN DIGITAL BREAST TOMOSYNTHESIS

This phantom-based study aimed to examine radiation dose from digital breast tomosynthesis (DBT) and digital mammography (DM) and to assess the potential for dose reductions for each modality. Images were acquired at 10-60 mm thicknesses and four dose levels and mean glandular dose was determined using a solid-state dosemeter. Eleven readers assessed image quality and compared simulated lesions with those on a reference image, and the data produced was analysed with the Friedman and Wilcoxon signed-rank tests. For a phantom thickness of 50 mm (typical breast thickness), DBT dose was 13 % higher than DM, but this differential is highly dependent on thickness. Visibility of masses was equal to a reference image (produced at 100 % dose) when dose was reduced by 75 and 50 % for DBT and DM. For microcalcifications, visibility was comparable with the reference image for both modalities at 50 % dose. This study highlighted the potential for reducing dose with DBT.

Radiation doses received in the United Kingdom breast screening programme in 2010 to 2012

OBJECTIVES

To review the radiation doses received by women attending the UK breast-screening programme between 2010 and 2012. To compare doses with previous years and to quantify the impact on dose of changing from analogue to digital imaging and to analyse doses by type of imaging system.

METHODS

Measurements of doses to samples of about 50-100 women attending for screening were collected across the whole of the UK breast-screening programme.

RESULTS

Data were collected for 87,122 exposures, using 449 X-ray sets, for 25,408 women. The average mean glandular dose (MGD) was 1.79 mGy for mediolateral oblique images and 1.58 mGy for craniocaudal images. The average MGD per two-view examination was 4.01 mGy for film-screen imaging and 3.03 mGy for direct digital radiography (DR) and 4.69 mGy for computed radiography.

CONCLUSION

The MGD to women attending breast screening has been reduced on average by about 25% where DR systems have replaced film-screen systems. The dose reduction was greatest for breasts with the largest compressed thickness. There are large variations in dose between the different models of DR system provided by different manufacturers. There should be further work to ensure that all DR systems are operated at the optimal dose level to ensure the best cancer detection while balancing the detriment caused by using radiation.

ADVANCES IN KNOWLEDGE

Changes in the radiation dose in breast screening over time have been determined. Specifically, the impact on radiation dose of introducing different types of DR and computed radiography system into breast screening has been quantified.

Patient doses from screen-film and full-field digital mammography in a population-based screening programme

The aim of this study was to compare mean glandular dose (MGD) in all full-field digital mammography (FFDM) and screen film mammography (SFM) systems used in a national mammography screening program. MGD from 31 screening units (7 FFDM and 24 SFM), based on an average of 50 women at each screening unit, representing 12 X-ray models (6 FFDM and 6 SFM) from five different manufacturers were calculated. The MGD was significantly lower for FFDM compared with SFM (craniocaudal): 1.19 versus 1.27 mGy, respectively, mediolateral oblique: 1.33 versus 1.45 mGy, respectively), but not all of the FFDM units provided lower doses than the SFM units. Comparing FFDMs, the photon counting scanning-slit technology provides significantly lower MGDs than direct and indirect conversion digital technology. The choice of target/filter combination influences the MGD, and has to be optimised with regard to breast thickness.

Digital breast tomosynthesis versus digital mammography: a clinical performance study

OBJECTIVE

To compare the clinical performance of digital breast tomosynthesis (DBT) with that of full-field digital mammography (FFDM) in a diagnostic population.

METHODS

The study enrolled 200 consenting women who had at least one breast lesion discovered by mammography and/or ultrasound classified as doubtful or suspicious or probably malignant. They underwent tomosynthesis in one view [mediolateral oblique (MLO)] of both breasts at a dose comparable to that of standard screen-film mammography in two views [craniocaudal (CC) and MLO]. Images were rated by six breast radiologists using the BIRADS score. Ratings were compared with the truth established according to the standard of care and a multiple-reader multiple-case (MRMC) receiver-operating characteristic (ROC) analysis was performed. Clinical performance of DBT compared with that of FFDM was evaluated in terms of the difference between areas under ROC curves (AUCs) for BIRADS scores.

RESULTS

Overall clinical performance with DBT and FFDM for malignant versus all other cases was not significantly different (AUCs 0.851 vs 0.836, p = 0.645). The lower limit of the 95% CI or the difference between DBT and FFDM AUCs was -4.9%.

CONCLUSION

Clinical performance of tomosynthesis in one view at the same total dose as standard screen-film mammography is not inferior to digital mammography in two views.

Quantification of breast density with dual energy mammography: a simulation study

Breast density, the percentage of glandular breast tissue, has been identified as an important yet underutilized risk factor in the development of breast cancer. A quantitative method to measure breast density with dual energy imaging was investigated using a computer simulation model. Two configurations to measure breast density were evaluated: the usage of monoenergetic beams and an ideal detector, and the usage of polyenergetic beams with spectra from a tungsten anode x-ray tube with a detector modeled after a digital mammography system. The simulation model calculated the mean glandular dose necessary to quantify the variability of breast density to within 1/3%. The breast was modeled as a semicircle 10 cm in radius with equal homogenous thicknesses of adipose and glandular tissues. Breast thicknesses were considered in the range of 2-10 cm and energies in the range of 10-150 keV for the two monoenergetic beams, and 20-150 kVp for spectra with a tungsten anode x-ray tube. For a 4.2 cm breast thickness, the required mean glandular doses were 0.183 microGy for two monoenergetic beams at 19 and 71 keV, and 9.85 microGy for two polyenergetic spectra from a tungsten anode at 32 and 96 kVp with beam filtrations of 50 microm Rh and 300 microm Cu for the low and high energy beams, respectively. The results suggest that for either configuration, breast density can be precisely measured with dual energy imaging requiring only a small amount of additional dose to the breast. The possibility of using a standard screening mammogram as the low energy image is also discussed.

Breast cancer imaging: a perspective for the next decade

Breast imaging is largely indicated for detection, diagnosis, and clinical management of breast cancer and for evaluation of the integrity of breast implants. In this work, a prospective view of techniques for breast cancer detection and diagnosis is provided based on an assessment of current trends. The potential role of emerging techniques that are under various stages of research and development is also addressed. It appears that the primary imaging tool for breast cancer screening in the next decade will be high-resolution, high-contrast, anatomical x-ray imaging with or without depth information. MRI and ultrasonography will have an increasingly important adjunctive role for imaging high-risk patients and women with dense breasts. Pilot studies with dedicated breast CT have demonstrated high-resolution three-dimensional imaging capabilities, but several technological barriers must be overcome before clinical adoption. Radionuclide based imaging techniques and x-ray imaging with intravenously injected contrast offer substantial potential as a diagnostic tools and for evaluation of suspicious lesions. Developing optical and electromagnetic imaging techniques hold significant potential for physiologic information and they are likely to be of most value when integrated with or adjunctively used with techniques that provide anatomic information. Experimental studies with breast specimens suggest that phase-sensitive x-ray imaging techniques can provide edge enhancement and contrast improvement but more research is needed to evaluate their potential role in clinical breast imaging. From the technological perspective, in addition to improvements within each modality, there is likely to be a trend towards multi-modality systems that combine anatomic with physiologic information. We are also likely to transition from a standardized screening, where all women undergo the same imaging exam (mammography), to selection of a screening modality or modalities based an individual-risk or other classification.

[Mammographic evaluation of dense breasts: techniques and limits]

Breast density is a radiological concept based on the proportion of radiopaque glandular tissue relative to radiolucent fatty tissue. Mammographic evaluation of dense breasts is more difficult, related to technical difficulties, with decreased rates for detection and characterization of breast lesions, resulting in reduced sensitivity with increased number of interval cancers at routine follow-up when compared to radiolucent breasts. We will review the definition of dense breasts and their frequency, especially their relationship with the age of patients. We will discuss the current technical problems and the impact of breast density on the efficacy of conventional mammography. We will discuss the value of digital mammography, the role of computer assisted diagnosis (CAD) systems and tomosynthesis in the evaluation of dense breasts.

Clinical image quality criteria for full field digital mammography: a first practical application

In order to quantify the clinical quality of full-field digital mammography, a set of image quality parameters is developed. The set consisted of 12 image quality criteria and 8 physical characteristics of the image. The first set interrogates the visibility of anatomical structures and typical characteristics of a digital image, such as noise and saturation of dark and white areas. The second set of criteria evaluates contrast, sharpness and confidence with the representation of masses, microcalcifications and the image. The use of these criteria is reported in a retrospective study, in which the impact of dose on the radiological quality of digital mammograms is evaluated. Fifty patients acquired in a low-dose mode were retrieved and compared with 50 patients acquired in a dose mode that was set 41% higher. The dose affects, more than expected, contrast and sharpness of the image, whereas the visibility of the anatomical structures remains unchanged. With these parameters, quantification of the image quality is possible; however, because of subjectivity of the parameters, only intra-observer comparison and evaluation of the individual parameters rather than the overall results are advised. Together with physical tests of image quality, critical radiological evaluation of the quality should be included in the acceptance process of digital mammography.

Full-field digital mammography compared to screen film mammography in the prevalent round of a population-based screening programme: the Vestfold County Study

The purpose of the study was to compare the performance of full-field digital mammography (FFDM) with soft-copy reading to screen film mammography (SFM) used during the first prevalent 2-year round of population-based screening. A total of 18,239 women aged 50-69 years were screened with FFDM as part of the Norwegian Breast Cancer Screening Programme (NBCSP). Process indicators were compared to data from 324,763 women screened with SFM using the common national database of the NBCSP. The cancer detection rates were 0.77% (140/18,239) for FFDM and 0.65% (2,105/324,763) for SFM (p = 0.058). For ductal carcinoma in situ (DCIS) alone, the results were: FFDM 0.21% (38/18,239) compared to SFM 0.11% (343/324,763) (p < 0.001). Recall rates due to positive mammography were for FFDM 4.09% (746/18,239), while for SFM 4.16% (13,520/324,764) (p = 0.645), due to technically insufficient imaging: FFDM 0.22% (40/18,239) versus SFM 0.61% (1,993/324,763) (p < 0.001). The positive predictive value (PPV) in the FFDM group was 16.6% (140/843), while 13.5% (2,105/15,537) for SFM (p = 0.014). No statistically significant differences were recorded concerning histological morphology, tumour size, or lymph node involvement. In conclusion FFDM had a significantly higher detection rate for DCIS than SFM. For invasive cancers no difference was seen. FFDM also had a significantly higher PPV and a significantly lower technical recall rate.

Digital mammography: what do we and what don't we know?

High-quality full-field digital mammography has been available now for several years and is increasingly used for both diagnostic and screening mammography. A number of different detector technologies exist, which all have their specific advantages and disadvantages. Diagnostic accuracy of digital mammography has been shown to be at least equivalent to film-screen mammography in a general screening population. Digital mammography is superior to screen-film mammography in younger women with dense breasts due to its ability to selectively optimize contrast in areas of dense parenchyma. This advantage is especially important in women with a genetic predisposition for breast cancer, where intensified early detection programs may have to start from 25 to 30 years of age. Tailored image processing and computer-aided diagnosis hold the potential to further improve the early detection of breast cancer. However, at present no consensus exists among radiologists on which processing is optimal for digital mammograms. Image processing may also vary significantly among vendors with so far limited interoperability. This review aims to summarize the available information regarding the impact of digital mammography on workflow and breast cancer diagnosis.

Tomosynthesis and contrast-enhanced digital mammography: recent advances in digital mammography

Digital mammography is more and more replacing conventional mammography. Initial concerns about an inferior image quality of digital mammography have been largely overcome and recent studies even show digital mammography to be superior in women with dense breasts, while at the same time reducing radiation exposure. Nevertheless, an important limitation of digital mammography remains: namely, the fact that summation may obscure lesions in dense breast tissue. However, digital mammography offers the option of so-called advanced applications, and two of these, contrast-enhanced mammography and tomosynthesis, are promising candidates for improving the detection of breast lesions otherwise obscured by the summation of dense tissue. Two techniques of contrast-enhanced mammography are available: temporal subtraction of images acquired before and after contrast administration and the so-called dual-energy technique, which means that pairs of low/high-energy images acquired after contrast administration are subtracted. Tomosynthesis on the other hand provides three-dimensional information on the breast. The images are acquired with different angulations of the X-ray tube while the object or detector is static. Various reconstruction algorithms can then be applied to the set of typically nine to 28 source images to reconstruct 1-mm slices with a reduced risk of obscuring pathology. Combinations of both advanced applications have only been investigated in individual experimental studies; more advanced software algorithms and CAD systems are still in their infancy and have only undergone preliminary clinical evaluation.

United States radiological health activities: inspection results of mammography facilities

Purpose:

The Mammography Quality Standards Act (MQSA) was enacted in 1992 to set national standards for high-quality mammography, including standards for mammographic X-ray equipment, patient dose, clinical image quality, and related technical parameters. The MQSA also requires minimum qualifications for radiologic technologists, interpreting physicians and medical physicists, mandates acceptable practices for quality-control, quality-assurance, and requires processes to audit medical outcomes. This paper presents the findings of MQSA inspections of facilities, which characterize significant factors affecting mammography quality in the United States.

Materials and Methods:

Trained inspectors collected data regarding X-ray technical factors, made exposure measurements for the determination of mean glandular dose (MGD), evaluated image quality, and inspected the quality of the film-processing environment. The average annual facility and total U.S. screening exam workloads were computed using workload data reported by facilities.

Results:

Mammography facilities have made technical improvements as evidenced by a narrower distribution of doses, higher phantom-film background optical densities associated with higher phantom image-quality scores, and better film processing. It is estimated that approximately 36 million screening mammography exams were conducted in 2006, a rate that is almost triple the exam volume estimated for 1997. Digital mammography (DM) is now in use at approximately 14% (1,191 of 8,834) of MQSA-certified mammography facilities. The results indicate that DM can offer lower dose to the patient while providing comparable or better image quality.

Imaging breast cancer

Imaging has a significant role in diagnosing, treating, and monitoring breast cancer. Advances in this field are having a great impact in the clinical management of this disease. Breast cancer has now become an "outpatient cancer". This article describes the role and advances of imaging in breast cancer.