Room: Exhibit Hall | Forum 1
Purpose: To estimate the patient dose, it is important to note how the Average Glandular Dose (AGD) changes with different phantom thicknesses, as well as how the AGD differs between 2D and 3D modes. Another important aspect is to note the differences between the displayed and the measured AGDs to ensure an accurate estimation of patient dose.
Methods: Testing was done using Hologic Selenia Dimensions 3D and Hologic Selenia 2D Mammography Systems, and Hologic MultiCare Platinum Stereotactic Breast Biopsy (SBB). Variations of the technique were recorded for different BR-12 phantom thicknesses ranging from 2 cm to 8 cm, and for different compensation steps, using the 4 cm thickness. The displayed AGD was also noted for each thickness of phantom used, as well as the target and filter used. Measurements of the AGD were made using a RadCal 10X6-6M chamber and the ACR Mammographic Accreditation Phantom. When applicable, 2D and 3D displayed and measured AGD values were compared for the same setups and phantom thickness.
Results: For the Dimensions (2D & 3D modes) and SBB Units, the displayed AGD increased exponentially as the BR-12 phantom thickness increased. On the Hologic Selenia 2D, the displayed AGD increased linearly with the phantom thickness. When comparing the displayed AGD to the measured AGD, the percent differences ranged from 0.87% to 29.97%. At 2, 4, and 4.5 cm, the 3D AGD is greater than the 2D AGD, and, at 6 and 8 cm phantom thicknesses, the 3D AGD is less than the 2D AGD. The AGD changes linearly with the changing exposure compensation steps.
Conclusion: AGD varies with phantom thickness, target/filter combination, AEC compensation steps, and 2D/3D modes. Importing the data found into a dose estimation program can give a quick, automatic way to estimate the patient breast dose.