Congress:
EuroSafe Imaging 2017
Keywords:
Dosimetric comparison, Technical aspects, Radiation safety, Education, Mammography, Breast, Action 6 - Clinical audit tool for imaging, Action 3 - Image quality assessment based on clinical indications, Action 2 - Clinical diagnostic reference levels (DRLs), Action 4 - Quality of radiological equipment, Action 3 - Optimisation, diagnostic reference levels, image quality, Action 2 - Clinical audit
Authors:
D. Caramella, F. Paolicchi, G. Imbarlina, C. Marini, C. Sottocornola
DOI:
10.1594/esi2017/ESI-0031
Background/Introduction
The basic safety standards for exposure to ionizing radiation have been revised in the new European Directive 59/2013/EURATOM,
which must be implemented within February 2018.
The Directive promotes the commitment to a comprehensive information to the patient about the risks and benefits associated with exposure to ionizing radiation and that a dosimetric data referred to the exposure should be inserted in the radiological report.
Especially in the field of breast imaging,
the breast weight factors wT required for the calculation of the effective dose is increased from 0.05 to 0.12.
Standard Full-Field Digital Mammography (FFDM) is a fast and low-cost x-ray technique that involves relatively low doses of ionizing radiation,
and it is,
at present,
the only screening test that has been shown to reduce breast cancer-related mortality [1–2].
FFDM is used to assess potential abnormalities,
evaluate patients who have signs or symptoms of breast disease,
and provide follow-up of patients with probably benign findings.
A major limitation of this technique that depends on the total attenuation of the x-ray beam by the breast,
is the overlap of tissue which may obscure an area of interest and lead to a false-negative finding [3].
The introduction of FFDM has improved screen film mammography accuracy by avoiding the narrow range of linear response.
However,
FFDM still only acquires a 2D projection of a threedimensional (3D) object,
and it is not possible to overcome the fundamental limitation due to surrounding and overlying tissues which may impair a correct parenchyma visualization.
The advent of Digital Breast Tomosynthesis (DBT) may help to improve accuracy as a consequence of its ability to overcome this inherent limitation of FFDM caused by the overlapping of normal and pathological tissues.
With DBT,
the breast is compressed and held stationary between the compression paddle and the detector,
in a procedure similar to that used in FFDM.
However,
differently from 2D mammography,
tomosynthesis produces tomographic slices of an entire tissue volume during a single acquisition,
similar to a CT scan.
This is achieved by acquiring multiple low-dose projections of the breast during a limited angular rotation of the x-ray tube and then by calculating a 3D reconstruction [4-5].
The range of angles employed varies in different vendors’ implementations from 15° to 50° and the projection images are processed by reconstruction algorithms to produce a set of parallel slices,
normally with 1 mm thickness.
The acquisition geometry is not different from the one used in mammography,
and the only difference is that the x-ray tube is rotated in one plane around the compressed breast while multiple images are acquired.
During the acquisitions,
the detector can either be static or rotate to maintain its top surface perpendicular to the x-ray tube.
Due to the limited number of acquired projection angles,
tomosynthesis has anisotropic spatial resolution.
The total number of reconstructed images varies depending on the thickness of the compressed breast.
Images are usually displayed on a workstation as 2D slices,
which allow the radiologist to scroll through the individual images and set section thickness as thin as 1mm.
Different DBT systems received approval for clinical use around the world.
Until now,
however,
although there have been several studies comparing the diagnostic performances of single-view DBT or a combined technique with two-view FFDM [6-9],
there have been no studies comparing the respective radiation doses.
Therefore,
the aim of our study was to evaluate the radiation dose of a clinical DBT system for the acquisition of mammographic and tomosynthesis images.