Radiation Dose in 2D Mammography and 3D Tomosynthesis: A Buyer's Guide

What mean glandular dose actually measures

Mean glandular dose (MGD) is the quantity used to describe the radiation absorbed by the glandular tissue of the breast, which is the tissue of radiobiological interest. It cannot be measured directly in a patient, so it is estimated from the measured tube output, the beam quality (anode, filter and kVp), the compressed breast thickness and the breast composition, using published conversion factors.

Because of this, any quoted dose figure depends on the phantom or breast thickness used. A dose value without the thickness it refers to is not comparable between systems. When a supplier states a dose, ask for the equivalent thickness, the target and filter combination, and the detector used.

Mammography radiation dose in 2D digital systems

In a 2D digital examination the dose per view is governed mainly by the automatic exposure control (AEC), which selects kVp, target and filter and mAs according to the compressed thickness and density. A well-calibrated AEC keeps the detector signal constant while avoiding unnecessary exposure, so calibration at acceptance and during routine quality control matters as much as the hardware.

Compression also affects dose: firmer, even compression reduces breast thickness and scatter and lowers the dose needed for a given image quality. The Villa Melody IIID uses density-based automatic exposure control and the Smart Micro Press decremental compression system, two features that directly influence exposure per view.

3D mammogram: how much radiation is involved?

A tomosynthesis acquisition collects a series of low-dose projections over an arc and reconstructs thin slices. In general, the dose of a single tomosynthesis scan is of the same order as a 2D view, and national and international protocols set limits for it. The question of 3D mammography radiation dose equivalent therefore depends on what is acquired: tomosynthesis alone, 2D plus tomosynthesis in one compression, or tomosynthesis with a synthetic 2D image.

Combined 2D plus tomosynthesis acquisitions deliver more dose than either alone, because both exposures are made. Synthetic 2D images, reconstructed from the tomosynthesis data, are intended to remove the need for the second exposure. If dose is a priority, ask the supplier to confirm which acquisition modes the specific configuration supports and to provide measured MGD values for each.

• Tomosynthesis only, with or without a synthetic 2D image
• 2D plus tomosynthesis in a single compression
• Scan angle and number of projections, which influence both dose and depth resolution

Dose-related features to check on the Melody III line

The Melody IIID TS offers integrated tomosynthesis with three selectable scan angles (15°, 24° and 50°), an anti-scatter grid used during the scan and dynamic correction of the collimation field. With the optional Fast a-Se detector the scan times are listed as 2.5 s, 4 s and 7.7 s, which helps limit motion blur and patient time under compression.

The base Melody IIID can be configured with a-Si/CsI or a-Se detectors and upgraded in the field to tomosynthesis. Detector choice affects the dose needed for a given signal, so ask for dose and image-quality data for the exact detector you are specifying rather than for the product family.

Reference levels, QC and what to request from a supplier

Most programmes work with diagnostic reference levels, periodic MGD surveys and routine constancy tests. European protocols such as EUREF and the ACR programme both define acceptable and achievable dose levels for standard phantoms. Facility physicists should confirm which protocol applies in your emirate, and regulators such as FANR, MOHAP, DHA or DOH should be consulted for current requirements.

Before ordering, request the dose tables, AEC calibration procedure, the dose display (DICOM dose structured report if available) and the commissioning tests included in installation. A good supplier will support acceptance testing by your medical physicist rather than treat it as an afterthought. Beckfinity's specialists can supply the documentation and coordinate the installation and commissioning.

Practical conclusions for procurement teams

Compare systems on measured MGD at stated thicknesses, available acquisition modes, AEC behaviour in dense breasts and the quality of dose reporting. Related topics are covered in our guides to tomosynthesis explained and tomosynthesis for dense breasts. To discuss a configuration for your department, request a quote or consultation from Beckfinity.