Radiation doses in the UK trial of breast screening in women aged 40-48 years

Capability and reliability of deep learning models to make density predictions on low-dose mammograms

Purpose

Breast density is associated with the risk of developing cancer and can be automatically estimated using deep learning models from digital mammograms. Our aim is to evaluate the capacity and reliability of such models to predict density from low-dose mammograms taken to enable risk estimates for younger women.

Approach

We trained deep learning models on standard-dose and simulated low-dose mammograms. The models were then tested on a mammography dataset with paired standard- and low-dose images. The effect of different factors (including age, density, and dose ratio) on the differences between predictions on standard and low doses is analyzed. Methods to improve performance are assessed, and factors that reduce the model quality are demonstrated.

Results

We showed that, although many factors have no significant effect on the quality of low-dose density prediction, both density and breast area have an impact. The correlation between density predictions on low- and standard-dose images of breasts with the largest breast area is 0.985 (0.949 to 0.995), whereas that with the smallest is 0.882 (0.697 to 0.961). We also demonstrated that averaging across craniocaudal-mediolateral oblique (CC-MLO) images and across repeatedly trained models can improve predictive performance.

Conclusions

Low-dose mammography can be used to produce density and risk estimates that are comparable to standard-dose images. Averaging across CC-MLO and model predictions should improve this performance. The model quality is reduced when making predictions on denser and smaller breasts.

Breast Imaging Physics in Mammography (Part I)

Breast cancer is the most frequently diagnosed neoplasm in women in Italy. There are several risk factors, but thanks to screening and increased awareness, most breast cancers are diagnosed at an early stage when surgical treatment can most often be conservative and the adopted therapy is more effective. Regular screening is essential but advanced technology is needed to achieve quality diagnoses. Mammography is the gold standard for early detection of breast cancer. It is a specialized technique for detecting breast cancer and, thus, distinguishing normal tissue from cancerous breast tissue. Mammography techniques are based on physical principles: through the proper use of X-rays, the structures of different tissues can be observed. This first part of the paper attempts to explain the physical principles used in mammography. In particular, we will see how a mammogram is composed and what physical principles are used to obtain diagnostic images.

Setting Scottish diagnostic reference levels for mammography incorporating both craniocaudal and oblique projections between 30 and 80 mm

Optimisation must be carried out on all medical radiological units to ensure doses are as low as reasonably practicable, consistent with the intended purpose. To achieve this, population doses must be estimated and diagnostic reference levels (DRLs) set. For mammography examinations, mean glandular doses (MGDs) are calculated for this purpose. The average MGD per unit is compared to the national mammography DRL, which is applicable to compressed breast thicknesses (CBTs) of 50-60 mm for oblique (OB) views only and set using data from screening units. It is the purpose of this work to assess planar MGDs across Scotland and set DRLs based on data collected from all screening and symptomatic units across Scotland, considering craniocaudal (CC) and OB views and a wider range of CBTs. Data from the most recent dose audit (spanning 2015-2017) for 67 mammography x-ray units were collated and analysed (26 195 images). No large differences between MGD of CC and OB views were found when considering specific CBT ranges (median difference 2.6%). There was, however, a significant difference between screening and symptomatic data (19%). As expected, MGD increased with CBT and there were significant differences in MGD between manufacturers. From the data analysed, Scottish DRLs were set based on 95th percentile values for digital mammography units for three CBT ranges (30-49, 50-60 and 61-80 mm): 1.3, 1.8 and 2.6 mGy respectively. These values consider OB and CC views collectively. Fifth percentile values are quoted to highlight units at greater risk of insufficient image quality. These MGD values, together with image quality assessments, will facilitate optimisation across Scotland. Results show that use of different CBT ranges and inclusion of CC views increases the number of images included in dose audit data analysis from approximately 12%-92%, which is substantially more representative of the population.

INSTITUTIONAL BREAST DOSES IN DIGITAL MAMMOGRAPHY

The objective of this study was to survey breast dose in screening mammography, establish institutional doses and compare them with the corresponding dose values. Three hundred women between the ages of 40 and 80 years old participated in the study. All mammographic examinations were performed with a digital mammography system. The women characteristics (age, weight, height, BMI), technical and exposure parameters (anode/filter material, projection, compressed breast thickness (CBT), compression force, tube voltage, tube load), the entrance surface dose (ESD) and the average glandular dose (AGD) were recorded. The mean, median, 75th and 95th percentiles of the AGD and ESD distributions were estimated for all examinations, for right and left breast, as well as for CBT within 55-65 mm, for Cranio-Caudal (CC) and Medio-Lateral Oblique (MLO) projections. A statistical analysis was also performed, to investigate the impact of the recorded parameters on the ESD and AGD. The mean/median values of the ESD and AGD for all examinations, for CC and MLO projections were 4.60/4.29 and 5.42/5.25 mGy and 1.18/1.13 and 1.32/1.30 mGy, respectively. The mean/median values of the ESD and AGD for CC and MLO projections at CBT range 55-65 mm were 5.29/5.08 and 5.56/5.42 mGy and 1.30/1.24 and 1.36/1.32 mGy, respectively. The 75th percentile for CC and MLO projections were estimated 5.79 and 6.17 mGy, as well as 1.41 and 1.48 mGy in terms of ESD and AGD values, respectively. The 95th percentile of the ESD and AGD for CC and MLO projections were also 7.40 and 7.53 mGy and 1.76 and 1.78 mGy, respectively. The tube voltage, tube load, age and CBT had a significant influence on the dose values. The estimated values were found to be comparable, or in most cases lower, than the corresponding 75th and 95th percentile values from previous studies.

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.

Average glandular dose in digital mammography and digital breast tomosynthesis: comparison of phantom and patient data

For the evaluation of the average glandular dose (AGD) in digital mammography (DM) and digital breast tomosynthesis (DBT) phantoms simulating standard model breasts are used. These phantoms consist of slabs of polymethyl methacrylate (PMMA) or a combination of PMMA and polyethylene (PE). In the last decades the automatic exposure control (AEC) increased in complexity and became more sensitive to (local) differences in breast composition. The question is how well the AGD estimated using these simple dosimetry phantoms agrees with the average patient AGD. In this study the AGDs for both dosimetry phantoms and for patients have been evaluated for 5 different x-ray systems in DM and DBT modes. It was found that the ratios between patient and phantom AGD did not differ considerably using both dosimetry phantoms. These ratios averaged over all breast thicknesses were 1.14 and 1.15 for the PMMA and PMMA-PE dosimetry phantoms respectively in DM mode and 1.00 and 1.02 in the DBT mode. These ratios were deemed to be sufficiently close to unity to be suitable for dosimetry evaluation in quality control procedures. However care should be taken when comparing systems for DM and DBT since depending on the AEC operation, ratios for particular breast thicknesses may differ substantially (0.83-1.96). Although the predictions of both phantoms are similar we advise the use of PMMA  +  PE slabs for both DM and DBT to harmonize dosimetry protocols and avoid any potential issues with the use of spacers with the PMMA phantoms.

Conformance of mean glandular dose from phantom and patient data in mammography

In mammography dosimetry, phantoms are often used to represent breast tissue. The conformance of phantom- and patient-based mean glandular dose (MGD) estimates was evaluated mainly from the aspect of diagnostic reference levels. Patient and phantom exposure data were collected for eight diagnostic and three screening mammography devices. More extensive assessments were performed for two devices. The average breast thickness was close to the nationally used reference of 50 mm in diagnostic (50 mm, SD = 13 mm, n = 5342) and screening (47 mm, SD = 13 mm, n = 395) examinations. The average MGD for all breasts differed by 2% from the MGD determined for breasts in the limited compressed thickness range of 40-60 mm. The difference between phantom- and patient-based MGD estimations was up to 30%. Therefore, phantom measurements cannot replace patient dose data in MGD determination.

Estimating breast cancer mortality reduction and overdiagnosis due to screening for different strategies in the United Kingdom

Background:

The benefits and harms of population-wide mammography screening have been long debated. This study evaluated the impact of screening frequency and age range on breast cancer mortality reduction and overdiagnosis.

Methods:

We developed a Markov simulation model for the evaluation of mammography screening in a cohort of British women born in 1935–40.

Results:

For triennial screening in women aged 47–73, breast cancer mortality reduction and overdiagnosis was 18.1% (95% confidence interval: 17.3%, 19.0%) and 5.6% (5.1%, 6.1%), of all breast cancer deaths and diagnoses, respectively, from age 40 to 85 years. For annual screening in the same age range, estimates for both outcomes increased considerably to 35.0% (34.2%, 35.7%) and 7.6% (7.1%, 8.1%), respectively. For the age extension of triennial screening from 50–70 to 47–73, we estimated 5 (3, 7) incremental breast cancer deaths avoided and 14 (9, 19) incremental cases overdiagnosed per 10 000 women invited for screening.

Conclusions:

Estimates of mortality reduction and overdiagnosis were highly dependent on screening frequency, age range, and uptake, which may explain differences between some previous estimates obtained from randomised trials and from service screening.

Mammography equipment performance, image quality and mean glandular dose in Malta

In this first Maltese national mammography survey, the effectiveness of direct digital (DR) mammography in breast cancer screening has been confirmed. Patient data were made available from three clinics out of the participating nine. A dose survey of mean glandular dose (MGD) calculated for 759 patients examined in the state-owned mammography facilities was performed. An MGD national diagnostic reference level was set at 1.87 mGy for patients with breast compression thicknesses (BCT) between 5.0 and 7.0 cm. This range was selected since patient data were retrieved from three clinics only and the results showed that other international BCT reference levels may be unsuitable for the Maltese population. In fact, the overall average BCT was 5.75 ± 1.4 cm. The survey results have shown that the technical standard of mammographic equipment in the Malta National Breast Screening Programme is on a par with other countries, including its Western European counterparts.

Reconstruction of absorbed doses to fibroglandular tissue of the breast of women undergoing mammography (1960 to the present)

The assessment of potential benefits versus harms from mammographic examinations as described in the controversial breast cancer screening recommendations of the U.S. Preventive Task Force included limited consideration of absorbed dose to the fibroglandular tissue of the breast (glandular tissue dose), the tissue at risk for breast cancer. Epidemiological studies on cancer risks associated with diagnostic radiological examinations often lack accurate information on glandular tissue dose, and there is a clear need for better estimates of these doses. Our objective was to develop a quantitative summary of glandular tissue doses from mammography by considering sources of variation over time in key parameters, including imaging protocols, X-ray target materials, voltage, filtration, incident air kerma, compressed breast thickness, and breast composition. We estimated the minimum, maximum and mean values for glandular tissue dose for populations of exposed women within 5-year periods from 1960 to the present, with the minimum to maximum range likely including 90% to 95% of the entirety of the dose range from mammography in North America and Europe. Glandular tissue dose from a single view in mammography is presently about 2 mGy, about one-sixth the dose in the 1960s. The ratio of our estimates of maximum to minimum glandular tissue doses for average-size breasts was about 100 in the 1960s compared to a ratio of about 5 in recent years. Findings from our analysis provide quantitative information on glandular tissue doses from mammographic examinations that can be used in epidemiological studies of breast cancer.

Mammographic surveillance in women younger than 50 years who have a family history of breast cancer: tumour characteristics and projected effect on mortality in the prospective, single-arm, FH01 study

BACKGROUND

Evidence supports a reduction in mortality from breast cancer with mammographic screening in the general population of women aged 40-49 years, but the effect of family history is not clear. We aimed to establish whether screening affects the disease stage and projected mortality of women younger than 50 years who have a clinically significant family history of breast cancer.

METHODS

In the single-arm FH01 study, women at intermediate familial risk who were younger than 50 years were enrolled from 76 centres in the UK, and received yearly mammography. Women with BRCA mutations were not explicitly excluded, but would be rare in this group. To compare the FH01 cohort with women not receiving screening, two external comparison groups were used: the control group of the UK Age Trial (106,971 women aged 40-42 years at recruitment, from the general population [ie, average risk], followed up for 10 years), and a Dutch study of women with a family history of breast cancer (cancer cases aged 25-77 years, diagnosed 1980-2004). Study endpoints were size, node status, and histological grade of invasive tumours, and estimated mortality calculated from the Nottingham prognostic index (NPI) score, and adjusted for differences in underlying risk between the FH01 cohort and the control group of the UK Age Trial. This study is registered with the National Research Register, number N0484114809.

FINDINGS

6710 women were enrolled between Jan 16, 2003, and Feb 28, 2007, and received yearly mammography for a mean of 4 years (SD 2) up until Nov 30, 2009; surveillance and reporting of cancers is still underway. 136 women were diagnosed with breast cancer: 105 (77%) at screening, 28 (21%) symptomatically in the interval between screening events, and three (2%) symptomatically after failing to attend their latest mammogram. Invasive tumours in the FH01 study were significantly smaller (p=0·0094), less likely to be node positive (p=0·0083), and of more favourable grade (p=0·0072) than were those in the control group of the UK Age Trial, and were significantly less likely to be node positive than were tumours in the Dutch study (p=0·012). Mean NPI score was significantly lower in the FH01 cohort than in the control group of the UK Age Trial (p=0·00079) or the Dutch study (p<0·0001). After adjustment for underlying risk, predicted 10-year mortality was significantly lower in the FH01 cohort (1·10%) than in the control group of the UK Age Trial (1·38%), with relative risk of 0·80 (95% CI 0·66-0·96; p=0·022).

INTERPRETATION

Yearly mammography in women with a medium familial risk of breast cancer is likely to be effective in prevention of deaths from breast cancer.

Cost-effective screening for breast cancer worldwide: current state and future directions

Affordability of healthcare is highly limited by its skyrocketing cost. Access to screening and diagnostic medical equipment and medicine in developing countries is inadequate for the majority of the population. There is a tremendous worldwide need to detect breast cancer at its earliest stage. These needs must be balanced by the ability of countries to provide breast cancer screening technology to their populations. We reviewed the diagnostic accuracy, procedure cost and cost-effectiveness of currently available technique for breast screening and diagnosis including clinical breast examination, mammography, ultrasound, magnetic resonance imaging, biopsy and a new modality for cancer diagnostics termed elasticity imaging that has emerged in the last decade. Clinical results demonstrate that elasticity imaging even in its simplest and least sophisticated versions, like tactile imaging, has significant diagnostic potential comparable and exceeding that of conventional imaging techniques. In view of many countries with limited resources, effective yet less expensive modes of screening must be considered worldwide. The tactile imaging is one method that has the potential to provide cost-effective breast cancer screening and diagnostics.

Evaluation of the population dose to the UK population from the National Health Service Breast Screening Programme

In the United Kingdom National Health Service Breast Screening Programme (NHSBSP), women aged between 50 and 70 y are invited for mammography every 3 y. Screening histories for each woman, over four screening rounds, were analysed. Data from five screening programmes were used to select 57,425 women into the study. Cases were selected on the basis of being between the ages of 50 and 53 at the start of the NHSBSP (i.e. between 1989 and 1992). Assessment of the outcome for each screening round for each woman involved assigning a simple outcome code. Each of the possible pathways through the four screening rounds was analysed. This comprises of 500 possible pathways. This data enabled the following information to be determined: (i) The number of times a woman attended the screening programme. (ii) The number of women referred for assessment at each screening round. This information may be used to deduce the population dose to this group of women averaged over four screening rounds. Patient doses have been monitored since the programme's inception and are typically 4.5 mGy for two-view screening. It is possible to determine the mean glandular dose received by this cohort of women over four screening rounds by multiplying the number of examinations by the mean glandular dose for a typical woman. Allowance has to be made for the number of projections taken at each screening round. Once a woman has been screened, she may be invited back for further assessment if an abnormality is found on her mammogram. A stereotactic attachment is used to determine where to place the biopsy device. Although the dose received during a normal screening mammogram is well known, the dose for a stereotactic procedure and other assessment procedures is less well known, partly because only a small part of the breast is directly irradiated during stereotaxis. However, the woman may have multiple exposures during this stage. A prospective survey of doses was completed to deduce the mean glandular dose at the first assessment stage and during stereotaxis. Numbers of films, including magnification films taken at first-stage assessment were established in the North East of England and Scotland by means of a postal survey. Average total mean glandular dose was deduced using previous survey data for the screening programme and a multiplying factor to allow for magnification film dose. On average 1.6 full field and 0.15 collimated contact films are taken for each woman (with 2.25 and 0.75 mGy film(-1)), 1.0 full field and 0.9 collimated magnification views. The mean magnification film dose to the assessed breast was 5.0 and 1.7 mGy for a collimated magnification film. A survey of 134 women at screening centres in the North East of England was performed to deduce the mean glandular dose from digital stereotaxis which is almost universally used in breast screening. A typical woman received a dose to the assessed breast of 4.5 mGy with a range of 1.3-17 mGy. This data may be used to deduce the total mean glandular dose over four screening rounds including the assessment stages. The estimated mean glandular dose to a typical woman invited to the screening programme is approximately 16 mGy, when allowance for attendance rate and assessment rate over each screening round is made. The mean glandular dose to the population is approximately 4700 Sv y(-1).

Clinical management recommendations for surveillance and risk-reduction strategies for hereditary breast and ovarian cancer among individuals carrying a deleterious BRCA1 or BRCA2 mutation

BACKGROUND

In Canada, there are wide variations in services for patients at risk for hereditary breast and ovarian cancer (HBOC), and clinical interventions and recommendations differ between regions and/or provinces. National strategies for the clinical management of HBOC exist in the United Kingdom, France, and Australia, and clinical programs in Canada would benefit from similar national recommendations and a consistent approach to clinical management. The National Hereditary Cancer Task Force developed recommendations to address the clinical management of patients at high risk of HBOC and related cancers. These recommendations are based on current practice in high-risk cancer clinics that provide care for individuals with known BRCA1 or BRCA2 mutations.

METHODS

Canadian consensus recommendations were generated by the National Hereditary Cancer Task Force and compared mainly with two recently published guidance documents on the clinical management of women with increased risk of HBOC, one from the United Kingdom and the other from France. After review of these documents and the associated supporting scientific evidence, the Canadian consensus recommendations were modified and rated using predefined criteria.

CONCLUSIONS

These recommendations pertain to (1) surveillance options including breast self-examination, clinical breast examination, breast surveillance by imaging, ovarian cancer surveillance, and surveillance for men; (2) risk-reduction strategies including prophylactic mastectomy, prophylactic salpingo-oophorectomy, and pharmacoprevention; and (3) the use of exogenous hormones. Regular updates should occur as new evidence becomes available.

Risk factors for induction of breast cancer by X-rays and their implications for breast screening

In order to discuss the balance of benefit and radiation risk in a breast screening programme, it is necessary to have numerical values for the probability of breast cancer induction by X-rays, stratified by age. Various sets of such values have been used hitherto, mainly in relation to breast screening in the UK, both within the NHS Screening Programme and more generally for younger age groups. Further sets have recently been reported. These different sets of values are described and discussed, together with the effects of using additive or relative risk models, and the effect of using a dose and dose rate modifying factor (DDREF). Possible new radiation risk factors for breast cancer induction by X-rays, drawn from these sets, are identified. These are used to calculate fresh values of cancer detection/induction ratios, as an index of benefit/risk, for screening age women and for younger women with and without a family history of breast cancer.

Radiation benefit and risk at the assessment stage of the UK Breast Screening Programme

The balance between benefit and radiation risk in a breast cancer screening programme has received much attention at the initial screening stage. This paper extends that attention to first stage assessment, i.e. the first stage at which women are recalled for further investigation because of suspected lesions or other suspect film features, and prior to any biopsy. Numbers of films, including magnification films, taken at this stage, have been established in two UK regions by different methods. Average total mean glandular dose has been calculated using published data of dose per film from initial screening and a multiplying factor to allow for magnification film dose. It is concluded that the benefit/risk ratio is considerably higher at first stage assessment than at initial screening by a factor of between 4 and 9, because of the very much higher cancer detection rate in this well-defined sub-group of women. Qualitatively, this conclusion is unaffected by the quite wide variation between screening centres in the numbers of films taken at first stage assessment.

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

The study purpose was the comparison between doses delivered by a full-field digital mammography system and a screen/film mammography unit, both using the same type of X-ray tube. Exposure parameters and breast thickness were collected for 300 screen/film (GE Senographe DMR) and 296 digital mammograms (GE Senographe 2000D). The entrance surface air kerma (ESAK) was calculated from anode/filter combination, kV(p) and mAs values and breast thickness, by simulating spectra through a program based on a catalogue of experimental X-ray spectra. The average glandular dose (AGD) was also computed. Results showed an overall reduction of average glandular dose by 27% of digital over screen/film mammography. The dose saving was about 15% for thin and thick breasts, while it was between 30% and 40% for intermediate thicknesses. Full-field digital mammography dose reduction is allowed by wider dynamic range and higher efficiency of digital detector, which can be exposed at higher energy spectra than screen/film mammography, and by the separation between acquisition and displaying processes.

[Identification and management of hereditary breast-ovarian cancers (2004 update)]

BACKGROUND

Since the last recommendations, up to 2500 new references had been published on that topic.

METHODOLOGY

On the behalf of the health Minister, the Ad Hoc Committee consisted of 13 experts carried out a first version revisited by five additional experts who critically analyzed the first version of the report.

MAIN UPDATING

Breast and ovarian cancer seem to be associated with fewer deleterious mutations of BRCA1 and BRCA2 than previously thought. The screening of ovarian cancer is still not an attractive option while in contrast MRI may be soon for these young women with dense breast, the recommended option for breast cancer screening. The effectiveness of prophylactic surgeries is now well established. French position is to favor such surgeries with regard to a quality of life in line with the expected benefit, and providing precise and standardized process described in the recommendation.

CONCLUSIONS

Due to methodological flaws, the low power and a short follow-up of the surveys, this statement cannot however aspire to a high stability.

Screening mammography in women aged 40-49: is it time to change?

There is little doubt that significant benefits can accrue from carrying out screening mammography of women aged 40–49 in the setting of a highly quality assured service delivery. This will best be achieved using digital mammography to maximise detection rates and trained and high volume reading expert radiologists to apply economic cushions of optimising specificity as well as sensitivity in addition to utilising modern and accurate assessment and tissue sampling techniques that have evolved.

Mammographic screening before age 50 years in the UK: comparison of the radiation risks with the mortality benefits

Mammographic screening before age 50 years is less effective than at older ages and the associated radiation risks are higher. We estimated how many breast cancer deaths could be caused and how many could be prevented by a decade of annual two-view mammographic screening starting at ages 20, 30 and 40 years, respectively, in the UK; for all women, and for women with first-degree relatives affected with breast cancer. We extrapolated from a radiation risk model to estimate the number of radiation-induced breast cancer deaths, and used results from randomised trials, which suggest a reduction in breast cancer mortality of 10–20% in women invited to screening before age 50 years, to estimate the number of deaths that could be prevented. The net change in breast cancer deaths was defined as the number of radiation-induced deaths minus the number of prevented deaths. For all women, assuming a reduction in mortality from screening of 20%, a decade of annual screening was estimated to induce more deaths than it prevents if started at age 20 years and at age 30 years (net increase=0.86 and 0.37 breast cancer deaths, respectively, per 1000 women screened). The corresponding estimate for screening starting at age 40 years was a net decrease of 0.46 deaths/1000 women screened and a zero net change assuming a 10% mortality reduction. Results for women with first-degree relatives with breast cancer were generally in the same direction but, because their background incidence rates are higher, the net increases or decreases were greater. In conclusion, our estimates suggest that a decade of annual two-view mammographic screening before age 40 years would result in a net increase in breast cancer deaths, and that starting at age 40 years could result in a material net decrease only if breast cancer mortality is reduced by about 20% or more in women screened. Although these calculations were based on a number of uncertain parameters, in general, the conclusions were not altered when these parameters were varied within a feasible range.

Randomised controlled trial of mammographic screening in women from age 40: results of screening in the first 10 years

Debate continues over the effectiveness of screening by mammography in women below age 50. We report here on results of screening in the first 10 years of a randomised trial to study the effect on breast cancer mortality of invitation to annual mammography from age 40 to 41 compared to first invitation to the 3-yearly UK national programme at age 50-52. The trial is taking place in 23 NHS breast screening centres. Between 1991 and 1997, 160 921 women were randomised in the ratio 1 : 2 to intervention and control arms. Screening is by two views at first screen and single view subsequently; data on screening up to and including round five are now complete. Uptake of invitation to screening is between 68 and 70% at all but the latest screening rounds. Rates of referral for assessment are 4.6% at first screen and 3.4% at subsequent screens. Invasive cancer detection rates are 0.09% at first screen, and similar at rescreens until the sixth and later screens. There is little evidence of regular mammography in the trial control arm. The setting of this trial within the NHS breast screening programme should ensure applicability of results to a national programme.

Radiation doses received in the UK Breast Screening Programme in 2001 and 2002

The mean glandular doses (MGD) to samples of women attending for mammographic screening are measured routinely at screening centres in the UK Breast Screening Programme (NHSBSP). This paper reviews a large representative sample of dose measurements collected during screening in the NHSBSP in 2001 and 2002 for 53 218 films, using 290 X-ray sets, for 16 505 women. The average MGD was 2.23 mGy per oblique film and 1.96 mGy per craniocaudal film; similar to those found previously in the NHSBSP for the years 1997 and 1998. Increasing use of sophisticated units with automatic beam quality selection has reduced the radiation dose received by large breasts, with only 2% of oblique mammograms having doses in excess of 5 mGy. The increasing use of large format film has also reduced the doses to this sub-group. However the total dose per woman has increased due to the introduction of two view screening at every visit. The MGD to the standard breast was found to vary from 0.76 mGy to 2.29 mGy, with 97% of units below the recommended upper limit of 2 mGy, illustrating the benefit of strict quality control. A reduction in dose of 3% was observed between the age bands 50-54 years and 60-64 years. This study has confirmed that the proposed national diagnostic reference level (NDRL) of 3.5 mGy for 55 mm thick breasts is an appropriate value to identify systems giving unusually high doses, with just 3.5% of systems exceeding this level. In most cases these higher doses were explained by the design of one particular make of X-ray set and its mode of operation. Average doses for oblique views of average sized breasts were fairly well correlated with the dose to the standard breast, and typically 42% higher. This highlights the need for a revised definition of the standard breast used in the UK to better reflect the exposure factors and doses received in clinical practice.

Towards a proposition of a diagnostic (dose) reference level for mammographic acquisitions in breast screening measurements in Belgium

A diagnostic reference level (DRL) is a dose level for a typical X-ray examination of a group of patients with standard body sizes and for broadly defined types of equipment. These levels are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied. In this paper, we have calculated DRLs for screening mammography in Belgium. The 95th percentile of the mean average glandular dose is 2.46 mGy. The DRL based on polymethyl methacrylate (PMMA) measurements was 2.08 mGy. Correlation coefficient (R) between doses from patient studies and phantom studies was 0.90, with an average underestimation of the phantom measurements of 15% for systems that use only Mo/Mo anode/filter. For the centres that use other anode/filters, there is not enough scientific evidence that a single phantom measurement of a standard PMMA block is representative for the patient dose.

Patient dose in digital mammography

In the present investigation, we analyze the dose of 5034 patients (20,137 images) who underwent mammographic examinations with a full-field digital mammography system. Also, we evaluate the system calibration by analyzing the exposure factors as a function of breast thickness. The information relevant to this study has been extracted from the image DICOM header and stored in a database during a 3-year period (March 2001-October 2003). Patient data included age, breast thickness, kVp, mAs, target/filter combination, and nominal dose values. Entrance surface air kerma (ESAK) without backscatter was calculated from the tube output as measured for each voltage used under clinical conditions and from the tube loading (mAs) included in the DICOM header. Mean values for the patient age and compressed breast thickness were 56 years (SD: 11) and 52 mm (SD: 13), respectively. The majority of the images was acquired using the STD (for standard) automatic mode (98%). The most frequent target/filter combination automatically selected for breast smaller than 35 mm was Mo/Mo (75%); for intermediate thicknesses between 35 and 65 mm, the combinations were Mo/Rh (54%) and Rh/Rh (38.5%); Rh/Rh was the combination selected for 91% of the cases for breasts thicker than 65 mm. A wide kVp range was observed for each target/filter combination. The most frequent values were 28 kVp for Mo/Mo, 29 kVp for Mo/Rh, and 29 and 30 kV for Rh/Rh. Exposure times ranged from 0.2 to 4.2 s with a mean value of 1.1 s. Average glandular doses (AGD) per exposure were calculated by multiplying the ESAK values by the conversion factors tabulated by Dance for women in the age groups 50 to 64 and 40 to 49. This approach is based on the dependence of breast glandularity on breast thickness and age. The total mean average glandular dose (AGD(T)) was calculated by summing the values associated with the pre-exposure and with the main exposure. Mean AGD(T) per exposure was 1.88 mGy (CI 0.01) and the mean AGD(T) per examination was 3.8 mGy, with 4 images per examination on average. The mean dose for cranio-caudal view (CC) images was 1.8 mGy, which is lower than that for medio-lateral oblique (MLO) view because the thickness for CC images was on average 10% lower than that for MLO images. Mean AGD(T) for the oldest group of women (1.90) was 3% higher than the AGD(T) for the younger group (1.85) due to the larger compressed breast thickness of women in the older group (10% on average). Differences between the corresponding AGD(T) values of each age group were lowest for breast thicknesses in the range 40-60 mm, being slightly higher for the women in the older group.

Should women under 50 be screened for breast cancer?

Despite some controversy in recent years, the majority of experts agree on the evidence for effectiveness of breast screening by mammography for women aged 50 years and above, but for those under 50 years, the picture is much less clear. However, the issue remains of importance both to policy makers and to individual women; although the incidence of breast cancer is lower at younger ages, the life years lost due to cancers diagnosed below 50 years amount to a third of all those lost due to the disease.

A study of mean glandular dose during diagnostic mammography in Malaysia and some of the factors affecting it

The primary objective of this study was to determine the mean glandular dose (MGD) during diagnostic mammography in Malaysia. The secondary objective was to evaluate some of the factors affecting MGD. A survey of standard MGD was performed, based upon quality control records for the period October 1999 to August 2001. This covered 30 mammography units from 9 manufacturers. MGD was also measured for a series of patients attending mammography examinations at three other mammography units. MGD per film was estimated from recorded radiographic factors, the compressed breast thickness (CBT) and X-ray unit calibration data. MGD per woman was calculated by summing the MGDs for all films, and averaging it over both breasts. 300 women drawn equally from three major ethnic groups, namely Malay, Chinese and Indian, took part in the study. The difference of MGD per woman between ethnic groups was tested for significance using non-parametric Kruskal-Wallis and median tests. The factors affecting MGD per woman were tested for significance using a multivariate analysis of variance. The MGD for the phantom was 1.23 mGy (range 0.22-2.39 mGy) while the mean patient based MGD per film was 1.54 mGy and 1.82 mGy for the craniocaudal and mediolateral oblique views, respectively. The mean MGD per woman was 3.37 mGy. It was also found that there is no significant difference in MGD per woman among the ethnic groups (p>0.05, Kruskal-Wallis test). However, on the multivariate test two factors, namely half value layer of the X-ray beam and (CBT), had a significant effect on MGD per woman (p<0.05). No significant relationships were seen between MGD per woman with respect to ethnicity, body mass index or age.

Two-view screening and extending the age range: the balance of benefit and risk

The UK Breast Screening Programme intends to introduce two-view screening on all screening rounds, and also to extend the normal screening age range at its upper end from the present 64 years to 70 years. The implications of these changes for cancer detection:induction ratios and for benefit/risk ratios are discussed. It is shown that both ratios remain much greater than 1.0 at all screening ages. This is also true for younger women, subject to provisos regarding starting ages for annual screening as described in previous papers. The requirements for optimization in a breast screening programme are also discussed. It is suggested that benefit (rather than the benefit/risk ratio) should be maximized provided that benefit exceeds risk.