This study evaluated trends in patient dose and compression force for screening digital (DR) mammography systems. The results of five audits (carried out in 2011, 2014, 2018, 2020 and 2022) were compared. For every audit, anonymised screening examinations from each system consisting of the standard craniocaudal (CC) and mediolateral oblique (MLO) views of both breasts were analysed. Exposure parameters were extracted from the Digital Imaging and Communications in Medicine (DICOM) header and the mean glandular dose (MGD) for each image was calculated. Trends in the distribution of MGD, compressed breast thickness, compression force and compression force per radiographer were investigated. The mean MGD per image (and mean compressed breast thickness) was 1.20 mGy (58 mm), 1.53 mGy (59 mm), 1.83 mGy (61 mm), 1.94 mGy (60 mm) and 2.11 mGy (61 mm) for 2011, 2014, 2018, 2020 and 2022 respectively. The mean (and standard deviation) compression force was 114 (32) N, 112 (29) N, 108 (27) N, 104 (24) N and 100 (23) N for 2011, 2014, 2018, 2020 and 2022 respectively. The mean MGD per image has increased over time but remains below internationally established Diagnostic Reference Levels (DRLs). This increase is primarily due to a change in the distribution of the different manufacturers and digital detector technologies, rather than an increase in the dose of the individual systems over time. The mean compression force has decreased over time in response to client feedback surveys. The standard deviation has also reduced, indicating more consistent application of force.

The use of hand-held dental X-ray units is increasing within Australia since their portability is advantageous in applications such as aged care. However, proximity of the operator to the X-ray unit raises radiation safety concerns. The aim of this study was to evaluate operator radiation exposure and methods of dose reduction for the Rextar X camera-style hand-held dental X-ray unit. Leakage and scattered radiation were measured using a solid state detector. Scatter was generated using a Perspex head phantom. Measurements of scattered radiation dose as a function of distance were made with and without a lead acrylic scatter shield (0.6 mm Pb equivalence at 100 kVp) attached to the X-ray unit. Without the scatter shield, doses to the operator from a single adult maxillary molar X-ray exposure were 0.69, 0.78 and 0.47 µGy at the left hand, right hand and eyes respectively. With the scatter shield attached, doses were reduced to 0.25, 0.12 and 0.15 µGy respectively, corresponding to a dose reduction of 64, 85 and 68%. The contribution from leakage radiation was insignificant in comparison. It is highly unlikely that an operator would reach occupational dose limits when using the Rextar X hand-held dental X-ray unit, even without the scatter shield in place. Nevertheless, it is strongly recommended that the scatter shield is attached to keep operator doses as low as reasonably achievable. Use of the scatter shield additionally ensures compliance with the Australian legislative requirement for a protective barrier and is considered a preferable alternative to X-ray protective clothing.

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.

INTRODUCTION:This work aims to explore radiation doses delivered in screening mammography in Australia, with a focus on whether compressed breast thickness should be used as a guide when determining patient derived diagnostic reference levels (DRLs).METHODS:Anonymized mammograms (52,405) were retrieved from a central database, and DICOM headers were extracted using third party software. Women with breast implants, breast thicknesses outside 20-110 mm and images with incomplete exposure or quality assurance (QA) data were excluded. Exposure and QA information were utilized to calculate the mean glandular dose (MGD) for 45,054 mammograms from 61 units representing four manufacturers using previously well-established methods. The 75th and 95th percentiles were calculated across median image MGDs obtained for all included data and according to specific compressed breast thickness ranges.RESULTS:The overall median image MGD, minimum, maximum were: 1.39, 0.19 and 10.00 mGy, respectively, the 75th and 95th percentiles across all units' median image MGD for 60 ± 5 mm compressed breast thickness were 2.06 and 2.69 mGy respectively. Median MGDs, minimum, maximum, 75th and 95th percentiles were presented for nine compressed breast thickness ranges, DRLs for NSW are suggested for the compressed breast thickness range of 60 ± 5 mm for the whole study and three detector technologies CR, DR, and photon counting to be 2.06, 2.22, 2.04 and 0.79 mGy respectively.CONCLUSION:MGD is dependent upon compressed breast thickness and it is recommended that DRL values should be specific to compressed breast thickness and image detector technology.

Purpose To evaluate the radiation dose derived from digital mammography (DM) and digital breast tomosynthesis (DBT) at different tube current-exposure time product (mAs) and at 6 phantom thicknesses from 10 to 60 mm. Materials and Methods A total of 240 DM and DBT cranio-caudal (CC) phantom images were acquired at each thickness and at four exposure levels (the baseline mAs, 50%, 25% and 12.5% the baseline mAs). The incident Air Kerma (K) at the surface of the phantoms was measured using a solid state dosimeter. Mean Glandular Doses (MGD) were calculated for both modalities (DM and DBT). Results DBT dose was greater than that of DM for all mAs at each phantom thickness. For a breast thickness of 50 mm (close to average sized breast), the dose for DBT (2.32 mGy) was 13% higher than that for DM (2.05 mGy). The results also show that the difference in MGD between DM and DBT was less for the thicker compared with the thinner phantom, this difference being approximately a factor of 2.58 at 10 mm compared with a factor of 1.08 at 60 mm. While the MGD increased with increasing phantom thickness for both modalities, the dose increase with DBT was less than for DM, with the difference between 10 and 60 mm being a factor of 7 for DM and 3 for DBT. Conclusion The radiation dose from DBT was higher than that of DM and the difference in dose between DM and DBT decreases as phantom thickness increases.

Poster: 2014 CSM / R-0127 / Direct half value layer measurements in mammography - is near enough good enough? by: J. Diffey 1, L. Cartwright2, J. Crocker1, J. Heggie3; 1Newcastle/AU, 2SYDNEY/AU, 3MELBOURNE/AU

This study measured reading workstation monitors and the viewing environment currently available within BreastScreen New South Wales (BSNSW) centres to determine levels of adherence to national and international guidelines. Thirteen workstations from four BSNSW service centres were assessed using the American Association of Physicists in Medicine Task Group 18 Quality Control test pattern. Reading workstation monitor performance and ambient light levels when interpreting screening mammographic images were assessed using spectroradiometer CS-2000 and chroma meter CL-200. Overall, radiologic monitors within BSNSW were operating at good acceptable levels. Some non-adherence to published guidelines included the percentage difference in maximum luminance between pairs of primary monitors at individual workstations (61.5 % or 30.8 % of workstations depending on specific guidelines), maximum luminance (23.1 % of workstations), luminance non-uniformity (11.5 % of workstations) and minimum luminance (3.8 % of workstations). A number of ambient light measurements did not comply with the only available evidence-based guideline relevant to the methodology used in this study. Larger ambient light variations across sites are shown when monitors were switched off, suggesting that differences in ambient lighting between sites can be masked when a standard mammogram is displayed for photometric measurements. Overall, BSNSW demonstrated good adherence to available guidelines, although some non-compliance has been shown. Recently updated United Kingdom and Australian guidelines should help reduce confusion generated by the plethora and sometimes dated nature of currently available recommendations.

OBJECTIVE:This preliminary study determines whether the absolute amount of breast compression in mammography varies between and within practitioners.METHODS:Ethics approval was granted. 488 clients met the inclusion criteria. Clients were imaged by 14 practitioners. Collated data included Breast Imaging Reporting and Data System (BI-RADS) density, breast volume, compression and practitioner code.RESULTS:A highly significant difference in mean compression used by different practitioners (p<0.0001 for each BI-RADS density) was demonstrated. Practitioners applied compression in one of three ways using either low, intermediate or high compression force, with no significant difference in mean compression within each group (p=0.99, p=0.70, p=0.54, respectively). Six practitioners showed a significant correlation (p<0.05) between compression and BI-RADS grade, with a tendency to apply less compression with increasing BI-RADS density. When compression was analysed by breast volume there was a wide variation in compression for a given volume. The general trend was the application of higher compression to larger breast volumes by all three practitioner groups.CONCLUSION:This study presents an insight into practitioner variation of compression application in mammography. Three groups of practitioners were identified: those who used low, intermediate and high compression across the BI-RADS density grades. There was wide variation in compression for any given breast volume, with trends of higher compression demonstrated for increasing breast volumes. Collation of further studies will facilitate a new perspective on the analysis of practitioner, client and equipment variables in mammography imaging.ADVANCES IN KNOWLEDGE:For the first time, it has been practically demonstrated that practitioners vary in the amount of compression applied to breast tissue during routine mammography.

Breast density calibrations and stability measurements were undertaken on digital mammography systems to investigate whether a single calibration could be used for extended periods. The results indicated that the calibration did not change over time and was the same for two units investigated. The daily mean pixel value per mAs (MPV/mAs) for five systems was recorded over 22 months and showed varying periods of stability up to more than a year. However, step changes in MPV/mAs were noted and resulted from, for example, detector re-calibration or replacement. During stable periods the MPV/mAs for the static units varied mostly by <±5

Both interactive thresholding tools and human visual assessment have been related to the risk of developing breast cancer. In this paper we explore the relationship between human assessment of area of dense tissue and the actual thickness of tissue in the breast by using a volumetric density technique to compute areas of dense tissue, varying the threshold below which areas of low density are discounted and observing the correlation with visual assessment of density at different thresholds. Based on analysis of thresholds used in the automated method, radiologists’ definition of a dense pixel is one in which the percentage of glandular tissue is between 10% and 20% of the total thickness of the compressed breast at that point.

Scattered photons degrade mammographic image quality, so, almost universally, a physical anti-scatter grid is used to limit their effect Physical grids are not completely effective in rejecting only scattered photons, so patient dose must be increased in order to maintain low levels of quantum noise The standard attenuation rate (SAR), a quantitative normalised representation of breast tissue for image analysis applications, incorporates a model of scatter, and a software correction of the image blurring arising from scatter within the image signal A tissue equivalent phantom is used to investigate the possibility, in terms of both image sharpness and noise, of replacing the physical grid with the software correction in the SAR Encouraging results are reported, software correction almost matching the performance of the grid, whilst maintaining a superior signal-to-noise ratio.

If breast density is to be incorporated into breast cancer risk prediction models, the technique used for measurement must be quantitative, accurate, objective and reproducible. We present a semi-automated method that has been used by three independent operators to measure glandular volume from the digitised mammograms of 29 women (116 images). Additionally, one operator used the method on 10 separate occasions on a sample of 24 images. Intra-observer variability was found to be acceptably low, with coefficients of variation ranging from 3.5 – 5.7% depending on mammographic view (intra-class correlation coefficient close to 1 in all cases). However, inter-observer variability was greater with significant differences in glandular volume recorded between observers. This was attributed to the method of breast edge detection. The development of a new automatic breast edge detection algorithm has resolved the issue. The average difference in glandular volume measurement between two independent operators in the cranio-caudal view is -0.89cm3 (95% confidence interval -2.77 – 0.99 cm3) using the new method, compared to 5.99cm3 (95% confidence interval 2.72 – 9.76 cm3) using the old method.

A common metric used to optimise digital mammography image acquisition is contrast-to-noise ratio. Using the standard attenuation rate (SAR), a quantitative normalised representation of breast tissue for image analysis applications, we demonstrate that the image contrast may be completely separated from the acquisition parameters, in particular the beam quality, used for acquisition. Optimising the contrast-to-noise ratio at acquisition is therefore suboptimal, since the contrast may be manipulated by post processing. A tissue equivalent phantom is used to investigate the variation in both signal-to-noise ratio, and image sharpness within the SAR images. The results show that the primary effect of varying the acquisition parameters through the various automated optimisation of parameter modes, and hence the mean glandular dose, is to vary the global contrast of the acquired image, an effect successfully mapped to a common normalised basis using the SAR. The signal-to-noise ratio and image sharpness are second order effects, and are therefore dominated by the global image contrast when image acquisition is optimised using the contrast-to-noise ratio.

Breast density is positively linked to the risk of developing breast cancer. Furthermore, the addition of breast density as an input to breast cancer risk prediction models has been shown to improve their predictive power. Such models are used in the management of women at high risk but could potentially be used to determine screening strategy. A stepwedge-based technique has been used to measure volumetric density from the mammograms of 1,289 women in the UK screening programme who additionally completed a questionnaire on risk-related factors. The sample had a mean age of 60.1 (range 48.0 – 78.0), a mean breast thickness of 59mm (range 21 – 102mm) and a mean volumetric breast density of 11% (range 0.5 – 58%). Using Pearson’s correlation coefficient, breast density was found to be significantly correlated with weight (r = -0.45), body mass index (r = -0.48), age (r = -0.13) and breast thickness (r =-0.65) at the p = 0.01 level. Absolute glandular volume was also found to be significantly correlated with these parameters although the extent of correlation was weaker.

The largest source of error in the estimation of volumetric breast density typically arises from inaccuracies in the measurement of breast thickness. We present a method which accounts for paddle tilt and show that the variation within the compressed breast region may be as much as 21.2mm in the chest wall to nipple direction. The system-indicated value of breast thickness results in an average underestimation of compressed breast volume of 10.5% which has implications for density measurement. Paddle deformation in the lateral direction is shown to be insignificant in comparison. A method of modelling the thickness at the breast periphery is presented with examples of the thickness maps generated.

Conventional risk models for the development of breast cancer use inputs such as age, weight, hormonal factors and family history to compute individual breast cancer risk. These are employed in the management of women at high risk. The addition of breast density as an input has been shown to improve the accuracy of such models. An improved risk model could facilitate risk-based population screening. However, in order to use breast density in risk models there is a need to employ objective methods for measuring the density. A feasibility study has been carried out to assess the practicality of using a stepwedge-based technique for measuring breast density from mammograms in the UK National Health Service Breast Screening Programme and to determine whether additional information, relevant to risk, can be collected by questionnaire. Preliminary results suggest that it is practical to use such a technique in the screening environment. In a sample of 100 women, the mean density was 27% (range 2 - 81%). A negative trend in breast density was observed with Body Mass Index.

The volume of dense breast tissue can be calculated from an x-ray mammogram by imaging a calibrated step-wedge alongside the breast and determining the compressed breast thickness. Previously published work used a step-wedge made of PTFE with a maximum height of 35mm, length 175mm and width 15mm. Although fulfilling all theoretical requirements, it can be difficult to find space on the film for a large step-wedge when examining bigger breasts. Furthermore, the step-wedge is lead-lined, making it heavy and difficult to attach to the bucky. A more compact aluminium step-wedge has been designed to overcome these limitations, and experiments have been carried out on a prototype to evaluate its performance. Initial results show that the maximum and minimum heights of the prototype step-wedge are inadequate to sufficiently cover the range of optical densities within a breast image at the higher and lower exposures required for 6cm and 2cm Perspex (>200mAs and <40mAs respectively). However, the step increment appears to be satisfactory. Analysis of the mean pixel value and standard deviation within Regions of Interest of varying size and position indicates an optimum step length of 3mm. A new step-wedge has been constructed with an improved specification informed by the evaluation of the prototype.