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Proceedings Paper

Angular dependence of mammographic dosimeters in digital breast tomosynthesis
Author(s): Lena R. Bradley; Ann-Katherine Carton; Andrew D. A. Maidment
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Paper Abstract

Digital Breast Tomosynthesis (DBT) is an emerging imaging modality that combines tomography with conventional digital mammography. In developing DBT dosimetry, a direct application of mammographic dosimetry has appeal. However, DBT introduces rotation of the x-ray tube relative to the dosimeter, thus raising questions about the angular dependence of mammographic dosimeters. To measure this dependence, two ionization chambers, two solid-stated detectors, and one photodiode were rotated relative to an incident Mo/Mo x-ray beam. In this isocentric DBT simulation, the signal of each dosimeter was studied over an angular range of 180° for tube voltages of 26 to 34 kV. One ionization chamber was then modeled numerically to study the response to various monoenergetic beams. The results show that all dosimeters underestimate dose to varying degrees; solid-state detectors show the greatest angular dependence while ionization chambers show the least. Correction factors were computed from the data for isocentric DBT images using projection angles up to ±25°; these factors ranged from 1.0014 to 1.1380. The magnitude of the angular dependence generally decreased with increasing energy, as shown with both the measured and modeled data. As a result, the error arising in measuring DBT dose with a mammographic dosimeter varies significantly; it cannot always be disregarded. The use of correction factors may be possible but is largely impractical, as they are specific to the dosimeter, x-ray beam, and DBT geometry. Instead, an angle-independent dosimeter may be more suitable for DBT.

Paper Details

Date Published: 23 March 2010
PDF: 10 pages
Proc. SPIE 7622, Medical Imaging 2010: Physics of Medical Imaging, 76225L (23 March 2010); doi: 10.1117/12.845369
Show Author Affiliations
Lena R. Bradley, The Univ. of Pennsylvania (United States)
Ann-Katherine Carton, The Univ. of Pennsylvania (United States)
Andrew D. A. Maidment, The Univ. of Pennsylvania (United States)


Published in SPIE Proceedings Vol. 7622:
Medical Imaging 2010: Physics of Medical Imaging
Ehsan Samei; Norbert J. Pelc, Editor(s)

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