Aims and objectives
The mean glandular dose (MGD) is the parameter used to estimate the amount of radiation dose absorbed by the breast during mammography.
MGD is calculated by multiplying the air-kerma measured at the breast surface entrance by appropriate conversion factors obtained from Monte Carlo calculations [1-3] or analytical models .
Depending on the considered model,
conversion factors count for the energy characteristics of the X-ray spectrum selected for breast exposure,
usually represented by the half value layer (HVL),
and for the breast absorption “properties”,
Methods and materials
A total of 20247 digital mammograms of 5076 patients (standard mammography consists of two projection images per breast,
4 images per patient) were acquired by six mammography units,
using the standard automatic exposure mode (AEC).
In Table 1 ,
the total number of patients and images are given per mammography equipment used.
All the images (raw data) were processed by Volpara 1.5.0 (Volpara,
NZ) and volumetric breast density (VBD),
the relative fraction of glandular tissue over the full breast volume,
The overall mean compressed breast thickness was (53.4 ± 14) mm,
with some differences among systems,
as illustrated in Fig. 3.
A significant difference (p < 0.0001) versus the other systems was found for the GE Senographe DS that has a smaller field-of-view (18 x 24 cm2) and therefore is used to image breasts limited in size,
and for the IMG Giotto Image 3DL which showed a miscalibration in the estimation of compressed breast thickness.
The distribution of breast glandularity obtained by Volpara confirmed results...
This study proved that dose values (MGD) provided by manufacturers,
using different models and assuming breast density a priori,
are significantly different compared to those obtained after accounting for real differences among breast densities,
now available processing images by suitable software tools.
Software packages for quantitative breast density assessment can also be used to estimate mean glandular dose more accurately,
allowing comparison of dosimetric data across manufacturers,
applying the same computational method and consistent assumptions.
Veneto Institute of Oncology IOV - IRCCS,
Elmory University School of Medicine,
Medical Physics Division,Castelfranco Veneto Hospital,
Medical Physics Division,“Città della Salute” Hospital,
Volpara Solutions Ltd,
“Additional factors for the estimation of mean glandular breast dose using the UK mammography dosimetry protocol”,
Phys Med Biol 45:3225-3240.
Normalized glandular dose (DgN) coefficients for arbitrary X-ray spectra in mammography: computer-fit values of Monte Carlo derived data,
Med Phys 29:869-875.
van Engen R.E.
Further factors for the estimation of mean glandular dose using the United Kingdom,
European and IAEA breast dosimetry protocols,
Phys Med Biol 54:4361-4372....