Abstract
Average glandular dose (AGD) in digital mammography crucially depends on the estimation of breast glandularity. In this study we compared three different methods of estimating glandularities according to Wu, Dance and Volpara with respect to resulting AGDs. Exposure data from 3050 patient images, acquired with a GE Senographe Essential constituted the study population of this work. We compared AGD (1) according to Dance et al. applying custom g, c, and s factors using HVL, breast thickness, patient age and incident air kerma (IAK) from the DICOM headers; (2) according to Wu et al. as determined by the GE system; and (3) AGD derived with the Dance model with personalized c factors using glandularity determined with the Volpara (Volpara Solutions, Wellington, New Zealand) software (Volpare AGD). The ratios of the resulting AGDs were analysed versus parameters influencing dose. The highest deviation between the resulting AGDs was found in the ratio of GE AGD to Volpara AGD for breast thicknesses between 20 and 40 mm (ratio: 0.80). For thicker breasts this ratio is close to one (1 ± 0.02 for breast thicknesses >60 mm). The Dance to Volpara ratio was between 0.86 (breast thickness 20–40 mm) and 0.99 (>80 mm), and Dance/GE AGD was between 1.07 (breast thickness 20–40 mm) and 0.98 (41–60, and >80 mm). Glandularities by Volpara were generally smaller than the one calculated with the Dance method. This effect is most pronounced for small breast thickness and older ages. Taking the considerable divergences between the AGDs from different methods into account, the selection of the method should by done carefully. As the Volpara method provides an analysis of the individual breast tissue, while the Wu and the Dance methods use look up tables and custom parameter sets, the Volpara method might be more appropriate if individual ADG values are sought. For regulatory purposes and comparison with diagnostic reference values, the method to be used needs to be defined exactly and clearly be stated. However, it should be accepted that dose values calculated with standardized models, like AGD and also effective dose, are afflicted with a considerable uncertainty budgets that need to be accounted for in the interpretation of these values.
Highlights
Breast cancer is the most common cancer in women worldwide and still shows high mortality
The ratios of GE Average Glandular Dose (AGD) and Dance AGD to Volpara AGD are shown in Fig. 3 as functions of breast thickness
As the calculated AGD depends crucially on the glandularity of the particular breast tissue, a reliable determination of this factor is of high importance in dosimetry
Summary
Breast cancer is the most common cancer in women worldwide and still shows high mortality. While the incidence rate is increasing, the survival rate has improved over the last 20–30 years[1] This effect is owed to screening programs which were primarily established in the western hemisphere to decrease mortality. Since the AGD cannot be measured directly, conversion factors depending on breast size, breast composition and x-ray spectrum have to be determined. Such conversion factors derived using Monte Carlo simulations on simplified breast models allow to calculate the AGD from measured Incident Air Kerma (IAK)[6]. The most commonly used conversion factors were determined by Dance et al.[8] and were adopted in most beast dosimetry implementations This formalism was based on simple breast models and originally provided www.nature.com/scientificreports/.
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