Spatial distributions and mean doses in a breast phantom under mammography, with W/Rh and W/Ag target/filter combinations, based on SSDs and XR-QA2

Abstract

The aim of this study was to evaluate the spatial distributions and mean doses using tissue equivalent (TE) materials for a breast phantom under direct digital mammography (MDR), with target/filter combinations of W/Rh and W/Ag, using XR-QA2 radiochromic films and solid-state detectors (SSDs). An external SSD, MDR, and a set of radiochromic films were used. First, the external SSD was positioned on the mammographic bucky and irradiated four times for each selected voltage and target/filter combination for calibration purposes. Then, 10 (W/Rh) and five (W/Ag) radiochromic films were exposed on top of the two acrylic plates of the mammographic bucky. The films placed on the breast phantom reproduced the exposure conditions of the SSD, at 28 kV and 40 mAs, with five expositions. The films were digitized, and the red-net color (red RGB component) intensities were converted into the mean and standard deviation of the optical density (OD). The mathematical correlations between OD and the exposure values (EXP) were calculated and compared with international and Brazilian national standards. The correlation between EXP and OD had a regression quality of higher than 0.99, with no systematic error. The mean doses for TE-glandular and TE-skin for target/filter combinations of W/Rh and W/Ag were below 1.5 mGy, i.e., within the tolerance level of the regulatory standards, and were equivalent to the exposure values of the MDR. Dosimetric maps were used to visualize the spatial dose distribution, and the results showed a certain heterogeneity, although this was close to the range of mean doses. The results for MDR-W/Rh and W/Ag met Brazilian national and international regulatory limits. We conclude that XR-QA2 radiochromic films are reliable for application to MDR-W/Rh and W/Ag and can depict the spatial dose distributions for TE-glandular and TE-skin.