Written by Kerstin Bailey
The purpose of this assignment is to create a research question that identifies a clinical issue and present a critique of evidence using literature reviews. I have chosen to discuss two breast cancer screening types; digital mammography (DM) and digital breast tomosynthesis (DBT). My research question is: Will the use of digital breast tomosynthesis (DBT) increase the effectiveness of screening for breast cancer in women in comparison to digital mammography (DM)? My aim is to critique this question through a series of literature reviews relevant to breast cancer within New Zealand. I aim to research and understand the rationale for the following; diagnostic accuracy and early detection using DBT, reduction in false positive findings and recalls, time taken and radiation dose required and lastly sensitivity for the patient.
The rationale for choosing breast cancer screening as my clinical issue lies in the fact that this cancer is the most prevalent form of the disease amongst women in New Zealand. Each year roughly 2800 women are diagnosed and around 650 women die from breast cancer. One in nine women in New Zealand will develop breast cancer at some stage of their lives. (Southern Cross, 2012). Majority of these women are aged 50 and over. A significant health concern is that in New Zealand Pacific and Maori women are at a greater risk of mortality from breast cancer than other ethnicities. They often present themselves too late for successful treatment and the breast cancer is well advanced (The New Zealand Breast Cancer Foundation, 2012). To help women have a better chance of surviving breast cancer, a breast screening programme was established.
Breast Screen Aotearoa was launched in New Zealand in December 1998 (Quilliam, 2013). Screening for breast cancer does not stop a person from getting the disease, but does lower their chance of death. If under the age of 50, breast screening reduces the chance of dying by 20 percent, if aged 50-65 by, 30 percent and between 65-69 years, it is reduced by approximately 45 percent (Ministry of Health, 2011).
The conventional method to screen for breast cancer is the X-ray mammogram which is performed by a radiographer. Each breast is placed between two plates on the X-ray machine which help to hold the breast securely while the pictures are taken. Some women think the process is uncomfortable and a few individuals find it painful. Some women hate the feeling, and this could stop them from going through with the test. The mammogram does not harm the breasts (Ministry of Health, 2011).
Women can have a screening mammogram free of charge every two years through Breast Screen Aotearoa if you meet the criteria. You have to be aged 45-69 years old, have no symptoms of breast cancer, have not had a mammogram within the last 12 months, not be pregnant or breastfeeding and qualify for public health services in New Zealand. If you currently or in the past have had breast cancer, you can re-enter the programme five years from when the cancer was found. Mammograms are however more beneficial for women between the ages of 50-69 years for two reasons. Firstly, breast tissue is denser in women under 50 making it harder to see if there are abnormalities in the tissue. Secondly, a false positive result is more frequent in women aged below 50 which could lead to more unnecessary tests (Ministry of Health, 2011). A mortality review of Breast Screen Aotearoa is being carried out to judge how effective breast screening has been since the beginning of the programme, with results due within the next two years (Quilliam, 2013).
My rationale for choosing to compare DM to DBT is to identify the limitations of DM and highlight the advantages of using DBT for more effective screening and saving of lives. Firstly, during DM the compression of the breasts can be uncomfortable and can defer women from getting the breast screening. Secondly, the compression causes overlapping of breast tissue which can hide the breast cancer causing it to not show in the mammogram (false negative reading). Mammograms only take one picture across the breasts from side to side and top to bottom. A DM administers a higher dose of radiation during the procedure opposed to DBT (Vroomen-Durning, 2012).
Digital breast tomosynthesis is a considerable advancement in digital mammography technology as it provides a more in depth analysis of breast tissue. t. DBT creates a 3D picture of the breast using x-rays. Multiple x-ray pictures of each breast are taken from various angles. The breast is placed the same way as a normal mammogram but with less pressure applied. The x-ray tube travels in an arc around the breast while 11 images are taken. The sequence of images then appears on a computer where they come together to create a series of clear highly focused 3D images all the way through the breast (Breastcancer.org, 2012).
There is a consensus among researchers that DBT is a more effective tool in identifying cancerous tissue in the breast while at the same time providing a more comfortable diagnostic experience for women. (Breastcancer.org, 2012). Through the use of various literature reviews I have further critiqued this method of breast screening to support my points of discussion.
DBT is considered to be a new promising method to create detailed images of breast tissue (Skanne, 2012). The detail lies in the digital outputs being reconstructed at 1mm intervals and presented as thin slices. This enables the margins and shape of breast masses to be more clearly defined by reducing overlapping tissue. The article concluded that DBT has the potential to improve breast cancer screening because of the increased detection of subtle breast cancers due to clearly defined images (Skanne, 2012).
The accuracy of DM alone in comparison to DM with the addition of DBT was assessed by Michell et al. (2012). In this study women who had been screened using DM were recalled for a comparison screening using DM and DBT. Seven hundred and thirty-eight women participated in the study with 26.8% diagnosed with malignant tumours, 37.68% as benign and 35.4% as normal. Some women were found to have more than one abnormality. The study indicates that DBT may increase the effectiveness and efficiency of screening. This is because the DBT 3D image provides better visualization of normal and benign features. The DBT image outputs were clearer than DM images having less “anatomical noise” i.e. less white blurry streaks. This allows radiologists to confidently diagnose whether the features are abnormal or normal (Michell, et al., 2012).
As indicated by Michell et al (2012), DBT has a higher accuracy when diagnosing due to the clearer image. It is suggested that by using a combination of 3D imaging (DBT) and 2D imaging (DM) that it will reduce recall rates and false positive findings (Skanne, 2012) . This will reduce the incidences of women suffering the anxiety and inconvenience of a recall and/or being incorrectly diagnosed. In the early diagnosis of this disease there is a prevalence of, and risk for depression and anxiety (Burgess, et al., 2005). Therefore it is important to reduce the chances of false positive recalls and thus the possible occurrence of anxiety and depression.
In addition to reducing the chances of false diagnosis, DBT can simultaneously increase cancer detection (Houssami & Skaane, 2013). Early detection of abnormalities in the breast tissue means the patient can be treated sooner, possibly saving their life.
DBT obtains 11 images (slices) over 7-19 seconds from one or two views. As the x-ray tube moves in a 15° arc across the breast, the x-rays are reconstructed into 1mm slices which can be observed as a 3D image (Skanne, 2012). The amount of time needed for the examination and acquisition of the images may take longer than 2 standard views and possibly increase the amount of dose.
The dose has been reported to be similar or slightly higher which varies between 1.66 and 1.90mGy compared to DM which ranges between 1.37 and 1.57mGy, whereas other papers have reported DBT to be similar or less than DM (Houssami & Skaane, 2013). However another study states that the mean glandular dose for a two-view DM is 3.7mGy and that DBT for one-view is 2.4mGy which shows a much greater reduction in dose, however the dose would increase if two views were carried out in DBT but due to the increase in sensitivity of DBT two views may not be required (Alakhras, et al., 2013). Radiation dose is dependent on several factors such as thickness of the breast tissue due to compression, and exposure factors.
Many women stay clear of mammography screening because of the pain from compressing their breasts. However, DBT requires a reduced amount of compression. This is because it is not required to compress and broaden the breast tissue with this procedure. The main intention for compression during DBT is to attain restricted movement and lessen the radiation dose by limiting the breast thickness (Park, Franken, Garg, Fajardo, & Niklason, 2007). Several studies have stated that DBT can be completed with greater patient satisfaction with up to 50% less compression than that used during DM. The lower compression does not compromise the diagnosis and accuracy (Alakhras, et al., 2013).
Implications to practice
There are several implications to practice when it comes to using DBT for breast screening.
Special training is needed for positioning of the breast and how to use the device. A radiographer will be needed to complete the procedure.
-Special training will also be needed for other hospital staff so they can educate and advocate their patients.
It might take longer for a diagnosis because the image is of greater detail (3dimensional). The radiologist may need to spend longer analysing the image. Therefore, longer wait time for results.
Cost of equipment. The average cost of a DBT device is slightly higher than DM but still lower than a CT or MRI device. However, DBT may reduce recall rates which would be a large saving due to the reduction in biopsies and histopathology assessments (Alakhras, et al., 2013).
In conclusion DBT has a promising future in regards to breast cancer screening. Through various studies discussed in this essay it is clear that DBT has a greater accuracy at detecting abnormalities and cancer. DBT also showed a greater reduction in recall rates and false positive findings. This reduction will help fewer women from suffering the anxiety and inconvenience of a recall. The time taken to complete a DBT is less than a DM but the interpretation of the image and write up may take longer. The radiation doses are similar between DBT and DM. However, the dosage would increase if two views were carried out in DBT or for women with denser breast tissue. The DBT procedure is more comfortable for the patient as less compression of the breast is required. DBT in conjunction with DM will help in the diagnosis of early stage breast cancer.
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