Abstract
To present a parameterization method based on singular value decomposition (SVD), and to provide analytical parameterization of the mean glandular dose (MGD) conversion factors from eight references for evaluating breast tomosynthesis dose in the Mammography Quality Standards Act (MQSA) protocol and in the UK, European, and IAEA dosimetry protocols. MGD conversion factor is usually listed in lookup tables for the factors such as beam quality, breast thickness, breast glandularity, and projection angle. The authors analyzed multiple sets of MGD conversion factors from the Hologic Selenia Dimensions quality control manual and seven previous papers. Each data set was parameterized using a one- to three-dimensional polynomial function of 2-16 terms. Variable substitution was used to improve accuracy. A least-squares fit was conducted using the SVD. The differences between the originally tabulated MGD conversion factors and the results computed using the parameterization algorithms were (a) 0.08%-0.18% on average and 1.31% maximum for the Selenia Dimensions quality control manual, (b) 0.09%-0.66% on average and 2.97% maximum for the published data by Dance et al. [Phys. Med. Biol. 35, 1211-1219 (1990); ibid. 45, 3225-3240 (2000); ibid. 54, 4361-4372 (2009); ibid. 56, 453-471 (2011)], (c) 0.74%-0.99% on average and 3.94% maximum for the published data by Sechopoulos et al. [Med. Phys. 34, 221-232 (2007); J. Appl. Clin. Med. Phys. 9, 161-171 (2008)], and (d) 0.66%-1.33% on average and 2.72% maximum for the published data by Feng and Sechopoulos [Radiology 263, 35-42 (2012)], excluding one sample in (d) that does not follow the trends in the published data table. A flexible parameterization method is presented in this paper, and was applied to breast tomosynthesis dosimetry. The resultant data offer easy and accurate computations of MGD conversion factors for evaluating mean glandular breast dose in the MQSA protocol and in the UK, European, and IAEA dosimetry protocols. Microsoft Excel™ spreadsheets are provided for the convenience of readers.
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