Patient Specific Average Glandular Dose in Mammography
V Patel1*, R Highnam2, C Tromans2, R J Pizzutiello3, S Destounis4, (1) Upstate Medical Physics, Victor, NY, (2) Matakina Technology Limited, Wellington, New Zealand,(3) Landauer Medical Physics, Glenwood, IL, (4) Elizabeth Wende Breast Care, Rochester, NYSU-C-116-1 Sunday 1:00PM - 1:55PM Room: 116
Purpose: It is essential to keep the dose to the breast as low as possible during routine mammography screening while achieving high diagnostic quality images. Currently, mammography systems report average glandular dose (AGD) assuming a 4.5 cm compressed thickness, 50% glandular and 50% adipose tissue equivalent phantom and typical x-ray beam characteristics. In this paper, we estimate the AGD for specific breasts on specific mammography systems.
Methods: For 16 digital mammograms, the technique parameters such as kVp, mAs and compressed thickness were collected from the DICOM header. An automated software system (Volpara (R), Wellington, New Zealand) estimated breast glandularity by analyzing each digital mammogram. For the specific mammography systems used, entrance air kerma and half-value layer (HVL) was measured for various kVp and target/filter combinations at various compressed breast thicknesses. The patient-specific AGD was calculated from dose models developed by Dance et. al. These AGD estimates were compared with those generated by the mammography system.
Results: For the 16 mammograms that were analyzed, the calculated patient-specific AGD ranged from 1.99 ± 0.20 mGy to 3.73 ± 0.37 mGy for breasts with range of calculated glandularity (approximately 3% to 27%) and compression thickness (45 mm to 68 mm). Our preliminary results show that our estimated patient-specific AGDs differed from the AGD reported on the mammography system for each mammogram by an average of approximately 32%. The maximum difference between our estimated patient-specific AGD and the displayed AGD was approximately 46%.
Conclusion: Dose estimations implemented by manufacturers may underestimate the actual patient AGD significantly as they do not account for the specific breast tissue composition, compressed breast thickness or x-ray beam parameters of the specific mammography system used. Patient-specific dose estimates may give a better indication of the actual dose delivered, and therefore the risk to the patient.
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