Diagnostic Reference Levels for digital mammography in Australia

Aims: In 3 phases, this thesis explores: radiation doses delivered to women during mammography, methods to estimate mean glandular dose (MGD), and the use of mammographic breast density (MBD) in MGD calculations. Firstly, it examines Diagnostic reference levels (DRLs) for digital mammography in Australia, with novel focus on the use of compressed breast thickness (CBT) and detector technologies as a guide when determining patient derived DRLs. Secondly, it analyses the agreement between Organ Dose estimated by different digital mammography units and calculated MGD for clinical data. Thirdly, it explores the novel use of MBD in MGD calculations, suggesting a new dose estimation called the actual glandular dose (AGD), and compares MGD to AGD. Methods: DICOM headers were extracted from 52405 anonymised mammograms using 3rd party software. Exposure and QA information were utilised to calculate MGD using 3 methods. LIBRA software was used to estimate MBD for 31097 mammograms. Median, 75th and 95th percentiles were calculated across MGDs obtained for all included data and according to 9 CBT ranges, average population CBT, and for 3 detector technologies. The significance of the differences, correlations, and agreement between MGDs for different CBT ranges, calculation methods, and different density estimation methods were analysed. Conclusions: This thesis have recommended DRLs for mammography in Australia, it shows that MGD is dependent upon CBT and detector technology, hence DRLs were presented as a table for different CBTs and detectors. The work also shows that Organ Doses reported by vendors vary from that calculated using established methodologies. Data produced also show that the use of MGD calculated using standardised glandularities underestimates dose at lower CBTs compared to AGD by up to 10%, hence, underestimating radiation risk. Finally, AGD was proposed; it considers differences in breast composition for individualised radiation-induced risk assessment

An open environment CT-US fusion for tissue segmentation during interventional guidance.

Therapeutic ultrasound (US) can be noninvasively focused to activate drugs, ablate tumors and deliver drugs beyond the blood brain barrier. However, well-controlled guidance of US therapy requires fusion with a navigational modality, such as magnetic resonance imaging (MRI) or X-ray computed tomography (CT). Here, we developed and validated tissue characterization using a fusion between US and CT. The performance of the CT/US fusion was quantified by the calibration error, target registration error and fiducial registration error. Met-1 tumors in the fat pads of 12 female FVB mice provided a model of developing breast cancer with which to evaluate CT-based tissue segmentation. Hounsfield units (HU) within the tumor and surrounding fat pad were quantified, validated with histology and segmented for parametric analysis (fat: -300 to 0 HU, protein-rich: 1 to 300 HU, and bone: HU>300). Our open source CT/US fusion system differentiated soft tissue, bone and fat with a spatial accuracy of ∼1 mm. Region of interest (ROI) analysis of the tumor and surrounding fat pad using a 1 mm(2) ROI resulted in mean HU of 68±44 within the tumor and -97±52 within the fat pad adjacent to the tumor (p<0.005). The tumor area measured by CT and histology was correlated (r(2) = 0.92), while the area designated as fat decreased with increasing tumor size (r(2) = 0.51). Analysis of CT and histology images of the tumor and surrounding fat pad revealed an average percentage of fat of 65.3% vs. 75.2%, 36.5% vs. 48.4%, and 31.6% vs. 38.5% for tumors <75 mm(3), 75-150 mm(3) and >150 mm(3), respectively. Further, CT mapped bone-soft tissue interfaces near the acoustic beam during real-time imaging. Combined CT/US is a feasible method for guiding interventions by tracking the acoustic focus within a pre-acquired CT image volume and characterizing tissues proximal to and surrounding the acoustic focus

Effective radiation attenuation calibration for breast density: compression thickness influences and correction

<p>Abstract</p> <p>Background</p> <p>Calibrating mammograms to produce a standardized breast density measurement for breast cancer risk analysis requires an accurate spatial measure of the compressed breast thickness. Thickness inaccuracies due to the nominal system readout value and compression paddle orientation induce unacceptable errors in the calibration.</p> <p>Method</p> <p>A thickness correction was developed and evaluated using a fully specified two-component surrogate breast model. A previously developed calibration approach based on effective radiation attenuation coefficient measurements was used in the analysis. Water and oil were used to construct phantoms to replicate the deformable properties of the breast. Phantoms consisting of measured proportions of water and oil were used to estimate calibration errors without correction, evaluate the thickness correction, and investigate the reproducibility of the various calibration representations under compression thickness variations.</p> <p>Results</p> <p>The average thickness uncertainty due to compression paddle warp was characterized to within 0.5 mm. The relative calibration error was reduced to 7% from 48-68% with the correction. The normalized effective radiation attenuation coefficient (planar) representation was reproducible under intra-sample compression thickness variations compared with calibrated volume measures.</p> <p>Conclusion</p> <p>Incorporating this thickness correction into the rigid breast tissue equivalent calibration method should improve the calibration accuracy of mammograms for risk assessments using the reproducible planar calibration measure.</p

Breast compression across consecutive examinations among females participating in BreastScreen Norway

Objectives Breast compression is used in mammography to improve image quality and reduce radiation dose. However, optimal values for compression force are not known, and studies has found large variation in use of compression forces between breast centres and radiographers. We investigated breast compression, including compression force, compression pressure and compressed breast thickness across four consecutive full field digital mammography (FFDM) screening examinations for 25,143 subsequently screened women aged 50-69 years. Methods Information from women attending four consecutive screening examinations at two breast centres in BreastScreen Norway during January 2007 - March 2016 was available. We compared the changes in compression force, compression pressure and compressed breast thickness from the first to fourth consecutive screening examination, stratified by craniocaudal (CC) and mediolateral oblique (MLO) view. Results Compression force, compression pressure and compressed breast thickness increased relatively by 18.3%, 14.4% and 8.4% respectively, from first to fourth consecutive screening examination in CC view (p&lt;0.001 for all). For MLO view, the values increased relatively by 12.3% for compression force, 9.9% for compression pressure and 6.9% for compressed breast thickness from first to fourth consecutive screening examination (p&lt;0.001 for all). Conclusions We observed increasing values of breast compression parameters across consecutive screening examinations. Further research should investigate the effect of this variation on image quality and women’s experiences of discomfort and pain

Impact of errors in recorded compressed breast thickness measurements on volumetric density classification using volpara v1.5.0 software

Purpose: Mammographic density has been demonstrated to predict breast cancer risk. It has been proposed that it could be used for stratifying screening pathways and recommending additional imaging. Volumetric density tools use the recorded compressed breast thickness (CBT) of the breast measured at the x-ray unit in their calculation, however the accuracy of the recorded thickness can vary. The aim of this study was to investigate whether inaccuracies in recorded CBT impact upon volumetric density classification and to examine whether the current quality control (QC) standard is sufficient for assessing mammographic density. Methods: Raw data from 52 digital screening mammograms were included in the study. For each image, the clinically recorded CBT was artificially increased and decreased to simulate measurement error. Increments of 1mm were used up to ±15% error of recorded CBT was achieved. New images were created for each 1mm step in thickness resulting in a total of 974 images which then had Volpara Density Grade (VDG) and volumetric density percentage assigned. Results: A change in VDG was recorded in 38.5% (n= 20) of mammograms when applying ±15% error to the recorded CBT and 11.5 % (n= 6) were within the QC standard prescribed error of ±5mm. Conclusion: The current QC standard of ±5mm error in recorded CBT creates the potential for error in mammographic density measurement. This may lead to inaccurate classification of mammographic density. The current QC standard for assessing mammographic density should be reconsidered

On the Safety of Implanted Breast Prostheses in Accidental Impacts

The employment of breast silicone implants, both in aesthetic and reconstructive medicine, is widespread thanks to their recognized biocompatibility and durability. Some critical situations, for example, in the case of accidental impacts, may induce concerns by potential patients about their use. Dynamic tests reproducing frontal impacts at speeds up to 90 km/h, with anthropomorphic dummies carrying 330 cc prostheses and wearing safety belts, were conducted. Tests showed a significant probability of internal gel loss following implant damage at the highest speed. Moreover, considering that prostheses may remain implanted for many years, the effects of accelerated aging at 37 °C, 60 °C, 75 °C and 90 °C in physiological solution were also investigated. Tensile tests of the shell material and compressive tests of the full prosthesis showed evidence of variation in the prostheses’ mechanical characteristics after aging, which affects their stiffness, deformability and strength. These results stress the importance of medical investigations for possible damages of the implanted prostheses in the case of an accident

Diagnostic and Interventional Radiology in a breast centre

Topic of the thesis is the analysis of three key aspects of diagnostic and interventional radiology in a Breast Center: 1 - monitoring of the radiation dose delivered by mammography; 2 – integrated diagnostic approach conducted together by radiologists and surgeons (joint CORD; 3 - interdisciplinary meetings. Radiation dose monitoring Mammography is still considered the most effective imaging technique for the early detection of breast cancer and for mortality reduction. The parameter for estimating the absorbed dose is the average glandular dose. The purpose of this section of the thesis is to present the data collected from three mammography units in the period from January 1 to May 31. A dose monitoring software (TQM) was used that was able to automatically detect relevant indices from X-ray equipments and to analyze the data in terms of variability of dosimetric behaviours. The “joint CORD” In the period from January 16 to April 11, a weekly session handled by a junior breast surgeon and a senior Radiology resident (joint CORD) was established. The aim of this session was to optimize the path within the Breast Centre of the patients with urgent referral and nonspecific symptoms. In fact, for these patients it is likely that the final diagnosis can be already reached with a clinical breast examination and a breast ultrasonography. Twelve sessions of joint CORD were performed, that included 95 patients (average: 7.9 patients for each session). Of the 95 patients who had access to this service, 33 had an examination performed elsewhere with detection of suspicious nodules or were controls at 6 months of multiple fibroadenomatosis; 20 came for palpable lumps; 16 for unilateral or bilateral breast pain; 5 for mastitis; 5 for swelling / hyperemia or collection after QUART; 4 for secretion (milky); and 12 for various reasons (axillary swelling, screening prior hormonal therapies, skin nodule, adenoma of the nipple). Of the 95 patients, besides ultrasound and clinical breast examination, 24 (25.2%) underwent mammography, 6 (6.3%) underwent MRI, and 2 (2, 1%) underwent stereotactic biopsy. Twentythree US-guided cytological examinations were performed (24.2%): in 21 cases of nodules and in 2 cases of mammary secretions. The results of cytology were: 15 C2 (benign findings) with the conclusion of the diagnostic iter; 2 C3 (probably benign findings); 4 C1 (inadequate sampling). The joint CORD allowed patients to finish their diagnostic workup in a single access, thus dramatically reducing the time they spent in the breast imaging center. Interdisciplinary meetings Were conducted interdisciplinary meetings (with breast radiologists and surgeons) on a weekly basis starting from January 17. This section of the thesis analyzes the period from January 17 to March 27. The cases discussed were tabulated to analyze the most frequent causes of problems, possible solutions and improvements for clinical practice. Eleven meetings were held, discussing a total of 48 cases (average: 4.36 cases discussed per meeting). Of the 48 cases discussed, 11 (22.9%) did not reach a cyto-histological conclusive diagnosis, 9 (18.7%) had an underlying lack of communication between radiologists and surgeons, 8 (16.6%) required a further biopsy, 6 (12.5%) had an improper use of MRI , 5 (10.4%) required additional MRI, 3 (6.25%) required a shared decision between radiologists and surgeons, 2 (4.1%) had a PET inappropriately performed, 2 (4.1%) were considered inappropriate for surgical evaluation, and 1 (2.07%) required a new mammography