Policy Library Clinical Advantages of Digital Breast Tomosynthesis in Symptomatic Patients

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1 Policy Library Clinical Advantages of Digital Breast Tomosynthesis in Symptomatic Patients Version: 1 Approved by: Faculty of Clinical Radiology Council Date of approval: Click and type: day month and year, e.g. 12 February BREAST IMAGING MODALITIES Following the results of numerous international and national trials, the use of Digital Breast Tomosynthesis (DBT) in clinical radiology is gaining momentum, as an adjunct and potential replacement of standard 2D mammography for breast imaging in symptomatic women, and in breast cancer screening in asymptomatic women. 1 This paper explains the technologies, use of both and the relative advantages of DBT for certain clinical presentations D Mammography (MMG) A mammogram is an X-ray examination of the breast which enables the detection and diagnosis of breast diseases particularly breast cancer. For each examination two views of each breast are obtained. 1.2 Digital Breast Tomosynthesis (DBT) DBT is a relatively new application of digital tomography. It has been developed to attempt to overcome the limitations of standard 2D digital mammography. DBT is a valuable addition to the breast imaging techniques available and provides additional diagnostic information, which both increases the cancer detection rate, and decreases the false positive rate caused by superimposition of breast tissue that can impede interpretation by a clinical radiologist. DBT involves data acquisition during rotation of the X-ray tube in an arc over the breast, creating a set of tomographic images of the breast, and a 2D mammogram. The number of images generated will depend upon breast size and can be up to 400 images, compared to 4 images for a standard MMG. 1.3 Limitations of Standard 2D Mammography Whilst standard 2D MMG has undergone significant improvements over recent years, from analogue to computed radiography (CR) to digital radiography (DR), mammography has inherent limitations. This is due to the minimal or no differences in tissue density between breast cancer and normal breast tissue. Breast cancer detection on mammography relies on the clinical radiologist identifying subtle differences in density, asymmetries and architectural distortions. 1 Please note that men as well as women can be affected by breast cancer Level 9, 51 Druitt Street, Sydney NSW 2000, Australia Ph: Fax: Web: ranzcr@ranzcr.edu.au ABN Page 1 of 5

2 A standard MMG displays a 3D volume of breast tissue as a 2D image. It superimposes all breast tissues into a single image. This can create spurious findings and obscure cancers in dense breasts, therefore 2D MMG has reduced sensitivity for cancer detection in dense breasts. Furthermore, women with dense breasts are at a higher risk of breast cancer (shown in studies by Boyd 2 from Canada). Whilst high mammographic density is particularly prevalent in the pre-menopausal group prior to the natural involution of breast tissue that occurs during menopause, it is also noted in post-menopausal women, either those on HRT or those who have the genetic predisposition to dense breast tissue. There is a recognised association between the risk of breast cancer with increasing breast density and the reduced mammographic sensitivity for cancer detection. It is for this reason that in the USA it is becoming standard practice, and legislated in over 30 states, that mammographic breast density be reported, as a guide to the risk of breast cancer, and to the likely sensitivity (or insensitivity) of cancer detection on standard mammography. It is usual for the clinical radiologist to obtain additional targeted views of suspected abnormalities found on standard 2D MMG to differentiate between spurious findings caused by superimposed breast tissue and a cancer, and to more clearly demonstrate suspected abnormal findings. The targeted view separates out the overlying tissues and improves the clarity of the mammographic findings. DBT obviates the need for targeted views because it reduces potential errors created by tissue superimposition present in 2D MMG views. 1.4 Where Digital Breast Tomosynthesis Can Assist All women benefit from DBT, however it is especially beneficial for women with dense breasts, and patients with early cancers that are obscured in the conventional 2D MMG. DBT has been shown to be beneficial not only in increased cancer detection rates but also of showing the extent of a cancer, such as multifocal or multi-centric cancer, which involves more than one location in the breast. Accurate detection of the extent of a breast cancer is a prerequisite to effective treatment planning, and reduces the need for repeat surgery with associated morbidity and cost implications because a cancer has not been completely excised. Studies 3,4,5 have shown that DBT: Increases cancer detection Reduces recall rates for superimposition of breast tissue Reduces false positive rates Reduces the need for extra spot compression MMG. 2 Boyd, N et al. Mammographic Density and the Risk and Detection of Breast Cancer: N Engl J Med. 2007;356: Skaane et al. Comparison of Digital Mammography Alone and Digital Mammography Plus Tomosynthesis in a Populationbased Screening Program. Radiology. Volume 267: Number 1 April Houssami, N; STORM, a new dimension for mammography screening: Evidence of improved detection using integrated 2D and 3D mammography provides opportunity for Australia to lead screening trials. MJA. 2013;199(5)2. 5 Lockie, D et al; Evaluation of Digital Breast Tomosynthesis (DBT) in a Breast Screen assessment service. Journal of Medical Radiation Sciences. Volume 61, Issue Supplement S1, pages , Sept Page 2 of 5

3 Regarding radiation safety, the cumulative radiation dose for DBT is approximately equivalent to a standard mammogram, so the radiation dose of doing both mammography and DBT is doubled, however this is still within the accepted dose for diagnostic mammography. If a 2D MMG requires further targeted imaging then the total radiation dose the woman receives is similar.due to the advantages outlined above, manufacturers have started to incorporate DBT imaging with standard 2D DR mammogram units and market its use. Some new equipment has the dual capacity to do both mammography and DBT simultaneously and others perform the MMG and DBT sequentially. DBT is typically done in conjunction with a standard 2D mammogram. 2D views are required for the clinical radiologist to compare with the previous mammograms One manufacturer (Hologic) has FDA approval to implement 3D tomosynthesis alone and create a standard 2D MMG by synthesising the tomographic images. This reduces acquisition time and radiation dose. Other manufacturers have not yet achieved FDA approval for this technique. Clinical radiologists require the standard 2D MMG for comparison with previous mammograms. Over time this may change and be replaced by the synthesised 2D images from the DBT. In summary, the addition of DBT to standard 2D MMG provides superior diagnostic information to the clinical radiologist. This is expected to lead to a reduction in the number of ultrasound examinations required to assess the symptomatic breast, or spurious 2D mammographic findings. Additionally, improved sensitivity and specificity afforded by this technique will result in better surgical management due to more accurate diagnosis of tumour extent prior to surgery. 1.5 Breast Ultrasound Clinical radiologists use ultrasound: to assess a woman with breast symptoms; to characterise a lesion detected on 2D MMG or DBT or breast MRI; to guide a biopsy of a lesion where possible under ultrasound; and in some circumstances identify a cancer which may not be seen on MMG/DBT (occult). Ultrasound examines breast tissue using high frequency sound waves to produce images that are displayed on a computer screen. The image is a map of the acoustic properties of the tissues examined. Some breast cancers and cysts are obscured by dense glandular tissue and may not be visible on 2D MMG or DBT. These can be detected on ultrasound because they have different acoustic properties to normal breast tissue. The ultrasound allows the clinical radiologist to evaluate whether a lesion is solid, vascular, or infiltrating, and assists in determining size and the nature of the lesion. The clinical radiologist will then usually biopsy visible suspicious lesions under ultrasound guidance due to its ease of use and ability to visualise needle position during biopsy and thereby accurately target the lesion. Page 3 of 5

4 2. DIAGNOSTIC BREAST IMAGING EXAMINATION IN A SYMPTOMATIC PATIENT 2.1 Patient Journey, Medical Oversight and Reporting A woman will be referred for a mammogram and digital breast tomosynthesis and/or an ultrasound if symptoms have appeared, or there is a personal history of breast cancer, or the woman is otherwise at high risk of breast cancer. 6 On arrival at a practice a patient will be greeted at the reception desk by clerical staff, have her or his details checked, including standard identity checks, and determine whether or not they have been to the practice before. The patient s referral is reviewed by the clinical radiologist who decides on the protocol to be used, and whether standard protocol needs to be varied. A radiographer will greet the patient, explain the procedure and ask questions in regard to prior mammograms and personal or family history of breast disease. A questionnaire will also be filled in. The patient will then be provided with a gown to change into. 2D MMG and DBT images will then be acquired and reviewed by the clinical radiologist and compared with any previous imaging. To perform the mammogram the radiographer will position the patient s breasts, one at a time, between the two plates on the X-ray machine while X-rays are taken. Two standard views of each breast are performed, followed by DBT. The acquisition time will vary depending on factors including the size of the breasts, location of any lesions, any deformity from previous surgery, the woman s age and mobility, and ability to cope with compression. DBT creates a stack of thin adjacent images of the breast. The angle of acquisition varies with the manufacturer of the DBT machine. Some manufacturers of tomosynthesis equipment allow the standard MMG and DBT images to be acquired in the same compression without requiring re-positioning of the patient, however some do require the MMG and DBT to be done as separate acquisitions, with re-positioning of the breast between the images. These images are reviewed by a clinical radiologist to check positioning and adequacy. A working diagnosis is made at this time. The time taken for a mammogram of both breasts including patient questionnaire, consent, positioning and x-ray acquisition is very variable, but generally takes an average of 20 minutes. Adding DBT to this process generally increases the examination time by a further 5-10 minutes. DBT usually obviates the need for extra spot compression MMG views because of the abolition of superimposition artefact and clearer depiction of the breast tissue. Targeted magnification views are still required for the assessment of microcalcification. 6 Men can also develop breast cancer, however it is more common amongst women. Page 4 of 5

5 If a patient requires an ultrasound, the patient will be taken into the ultrasound room shortly after the MMG and DBT, for the convenience of the patient and expediency of diagnosis. The sonographer will scan the patient to investigate any findings that were detected by the clinical radiologist on the MMG or DBT or an area of symptom complaint. The clinical radiologist will attend the patient to review the ultrasound in real time (viewing images on the monitor with the patient still on the examination bed) to properly assess any significant or uncertain findings. The clinical radiologist will read and interpret the images from all modalities utilised in the diagnosis of the patient s condition and provide a report to the referrer. The interpretation and reading time for a DBT study is significantly longer than for a MMG and studies have shown this to be at least a 135% increase 7. A clinical radiologist is able to read and interpret, and compare a mammogram in several minutes, however DBT requires additional time to read and interpret, due to the increase in images (which may be up to 400) depending upon breast size. Therefore the addition of DBT results in an increase in the time taken by the clinical radiologist to interpret the images and produce a report. 7 BERNARDI, D et al. Application of breast tomosynthesis in screening: incremental effect on mammography acquisition and reading time. The British Journal of Radiology, 85 (2012), e1174 e1178 Page 5 of 5