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Proceedings Paper

Radiation dose from MDCT using Monte Carlo simulations: estimating fetal dose due to pulmonary embolism scans accounting for overscan
Author(s): E. Angel; C. Wellnitz; M. Goodsitt; J. DeMarco; C. Cagnon; M. Ghatali; D. Cody; D. Stevens; C. McCollough; A. Primak; M. McNitt-Gray
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Paper Abstract

Pregnant women with shortness of breath are increasingly referred for CT Angiography to rule out Pulmonary Embolism (PE). While this exam is typically focused on the lungs, extending scan boundaries and overscan can add to the irradiated volume and have implications on fetal dose. The purpose of this work was to estimate radiation dose to the fetus when various levels of overscan were encountered. Two voxelized models of pregnant patients derived from actual patient anatomy were created based on image data. The models represent an early (< 7 weeks) and late term pregnancy (36 weeks). A previously validated Monte Carlo model of an MDCT scanner was used that takes into account physical details of the scanner. Simulated helical scans used 120 kVp, 4x5 mm beam collimation, pitch 1, and varying beam-off locations (edge of the irradiated volume) were used to represent different protocols plus overscan. Normalized dose (mGy/100mAs) was calculated for each fetus. For the early term and the late term pregnancy models, fetal dose estimates for a standard thoracic PE exam were estimated to be 0.05 and 0.3 mGy/100mAs, respectively, increasing to 9 mGy/100mAs when the beam-off location was extended to encompass the fetus. When performing PE exams to rule out PE in pregnant patients, the beam-off location may have a large effect on fetal dose, especially for late term pregnancies. Careful consideration of ending location of the x-ray beam - and not the end of image data - could result in significant reduction in radiation dose to the fetus.

Paper Details

Date Published: 15 March 2007
PDF: 12 pages
Proc. SPIE 6510, Medical Imaging 2007: Physics of Medical Imaging, 65102C (15 March 2007); doi: 10.1117/12.713820
Show Author Affiliations
E. Angel, David Geffen School of Medicine at UCLA (United States)
C. Wellnitz, Mayo Clinic (United States)
M. Goodsitt, Univ. of Michigan (United States)
J. DeMarco, David Geffen School of Medicine at UCLA (United States)
C. Cagnon, David Geffen School of Medicine at UCLA (United States)
M. Ghatali, David Geffen School of Medicine at UCLA (United States)
D. Cody, U.T.M.D. Anderson Cancer Ctr. (United States)
D. Stevens, U.T.M.D. Anderson Cancer Ctr. (United States)
C. McCollough, Mayo Clinic (United States)
A. Primak, Mayo Clinic (United States)
M. McNitt-Gray, David Geffen School of Medicine at UCLA (United States)

Published in SPIE Proceedings Vol. 6510:
Medical Imaging 2007: Physics of Medical Imaging
Jiang Hsieh; Michael J. Flynn, Editor(s)

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