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Title: SU-G-IeP2-05: Effect of Localizer Type and Patient Off-Centering On CT Radiation Dose with Use of Automatic Tube Current Modulation

Abstract

Purpose: Apparent patient size in CT localizers varies with localizer type and patient positioning, resulting in variation in effective mAs as guided by Tube Current Modulation (TCM). Our aim was to investigate the effects of vertical off-centering on CTDI-vol when using different localizer types and TCM strengths. Methods: A CTDI body phantom was scanned using an abdominal protocol with three TCM strengths (Siemens Definition AS40, CAREDose4D; very weak, average, very strong). Data was acquired at 11 table height positions; with phantom center at isocenter and at 10 other positions between 142mm below and 53mm above. At each position, scans were acquired using 5 different localizer types: PA, AP, Lateral, PA+Lateral, and Lateral+PA. CTDI-vol was recorded for the 165 combinations of table height, localizer type, and TCM strength, and magnification factors measured from localizer images. Results: Magnification factors from AP and PA localizers ranged from 0.79–1.11 and 1.35–0.91, respectively from lowest to highest positions (highest with phantom located closest to X-ray tube), with a smaller impact when using Lateral, PA+Lateral, Lateral+PA localizer types, all of which behaved similarly. For an average TCM strength and PA localizer, CTDI-vol ranged from 75% higher to 12% lower than the isocenter value for the lowestmore » to highest table positions, respectively. For table positions ranging from lowest to highest, CTDI-vol ranged from −23% to 17% for AP, from −8% to 0.3% for lateral and from −7% to 1% for a combination of PA and Lateral in either order. Similar behavior was found for different TCM strengths, but effects were more pronounced for very strong compared with very weak modulation strengths. Conclusion: Patient off-centering substantially impacts radiation dose, which depends on the amount of vertical offcentering and type of the localizer used. The combination of PA and Lateral localizers is most robust against effects of patient off-centering.« less

Authors:
; ;  [1]
  1. Brigham and Women’s Hospital, Boston, MA (United States)
Publication Date:
OSTI Identifier:
22649358
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; COMPUTERIZED TOMOGRAPHY; GUIDE TUBES; MODULATION; PALLADIUM; PATIENTS; PHANTOMS; POSITIONING; RADIATION DOSES; X-RAY TUBES

Citation Formats

Ruan, C, Sodickson, A, and Hamberg, L. SU-G-IeP2-05: Effect of Localizer Type and Patient Off-Centering On CT Radiation Dose with Use of Automatic Tube Current Modulation. United States: N. p., 2016. Web. doi:10.1118/1.4957010.
Ruan, C, Sodickson, A, & Hamberg, L. SU-G-IeP2-05: Effect of Localizer Type and Patient Off-Centering On CT Radiation Dose with Use of Automatic Tube Current Modulation. United States. https://doi.org/10.1118/1.4957010
Ruan, C, Sodickson, A, and Hamberg, L. 2016. "SU-G-IeP2-05: Effect of Localizer Type and Patient Off-Centering On CT Radiation Dose with Use of Automatic Tube Current Modulation". United States. https://doi.org/10.1118/1.4957010.
@article{osti_22649358,
title = {SU-G-IeP2-05: Effect of Localizer Type and Patient Off-Centering On CT Radiation Dose with Use of Automatic Tube Current Modulation},
author = {Ruan, C and Sodickson, A and Hamberg, L},
abstractNote = {Purpose: Apparent patient size in CT localizers varies with localizer type and patient positioning, resulting in variation in effective mAs as guided by Tube Current Modulation (TCM). Our aim was to investigate the effects of vertical off-centering on CTDI-vol when using different localizer types and TCM strengths. Methods: A CTDI body phantom was scanned using an abdominal protocol with three TCM strengths (Siemens Definition AS40, CAREDose4D; very weak, average, very strong). Data was acquired at 11 table height positions; with phantom center at isocenter and at 10 other positions between 142mm below and 53mm above. At each position, scans were acquired using 5 different localizer types: PA, AP, Lateral, PA+Lateral, and Lateral+PA. CTDI-vol was recorded for the 165 combinations of table height, localizer type, and TCM strength, and magnification factors measured from localizer images. Results: Magnification factors from AP and PA localizers ranged from 0.79–1.11 and 1.35–0.91, respectively from lowest to highest positions (highest with phantom located closest to X-ray tube), with a smaller impact when using Lateral, PA+Lateral, Lateral+PA localizer types, all of which behaved similarly. For an average TCM strength and PA localizer, CTDI-vol ranged from 75% higher to 12% lower than the isocenter value for the lowest to highest table positions, respectively. For table positions ranging from lowest to highest, CTDI-vol ranged from −23% to 17% for AP, from −8% to 0.3% for lateral and from −7% to 1% for a combination of PA and Lateral in either order. Similar behavior was found for different TCM strengths, but effects were more pronounced for very strong compared with very weak modulation strengths. Conclusion: Patient off-centering substantially impacts radiation dose, which depends on the amount of vertical offcentering and type of the localizer used. The combination of PA and Lateral localizers is most robust against effects of patient off-centering.},
doi = {10.1118/1.4957010},
url = {https://www.osti.gov/biblio/22649358}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}