01 February 2016
Digital breast tomosynthesis (DBT), otherwise known as 3-D mammography is state of the art technology that can increase the detection of small breast cancers. This new technique has now been investigated for breast screening patients in the UK (TOMMY Trial) and several European Breast Units. In the Oslo Tomosynthesis Screening Trial, the addition of DBT increased the invasive cancer detection rate by as much as 40%. Digital breast tomosynthesis is also good at ruling out cancer and in the majority of the trials fewer women were recalled for unnecessary biopsies.
The system works by creating a 3-D picture of the breast with X-rays. This improves the accuracy of mammography by reducing the inevitable overlap of breast tissue in which small masses and distortions can be hidden. These architectural changes, which may indicate a cancerous process, become much more visible on the tomosynthesis images. Although beneficial for all patients, as demonstrated in the UK TOMMY Trial, digital breast tomosynthesis is especially useful in women with dense breasts.
Breast tissue is made up of glandular, fibrous and fatty elements and some women have lots of fibrous and glandular material in the breast and very little fat. This increases the breast density and can make conventional mammograms difficult to interpret and therefore less precise. Women in their 20s, 30s and 40s often have naturally dense breast tissue. As women get older, those whose breast tissue remains dense seem to have a moderately increased risk of breast cancer, which is independent of other breast cancer risk factors.
Any patient with a new breast symptom should see their GP and will usually be referred to see a breast specialist. At that appointment, the specialist will examine the patient and then arrange the investigations. In the Maidstone and Tunbridge Wells catchment area, women over the age of 35 are advised to have standard 2-view mammograms with or without a breast ultrasound as part of the ‘one-stop’ assessment.
At present, in the few NHS units that have digital breast tomosynthesis it is recommended that patients should have 2-view mammograms and only proceed to DBT if advised by a breast radiologist. Other providers can offer breast tomosynthesis to all women requiring mammograms if requested by their consultant breast surgeon. This is often easier, and more comfortable, as the machine can take the 2-view and 3-D pictures with the patient in the same position. This avoids a wait whilst the radiologist reads the 2-view images and a second visit to the mammogram machine if necessary.
Having 2-view mammograms as well as DBT will effectively double the radiation dose received by the breasts. However, we all live with natural or ‘background’ radiation, which is present in our environment. A standard 2-view mammogram is estimated to be equivalent to 7 weeks of background radiation or a long-haul flight to Australia and back. So, the risk of the mammogram X-rays actually causing a breast cancer is extremely low. The DBT software can generate synthetic 2-view images and in the future these may be used instead of the extra breast exposures and consequently significantly reduce the radiation dose that breasts receive with mammography.
There is an increasing body of evidence, which indicates that DBT is a better test for breast cancer than conventional 2-view mammography. As such, DBT is a very welcome addition to the diagnostic toolbox and will help specialists detect more breast cancer in the early stages of the disease.