Comparison of effective dose using constant conversion, SSDE and patient specific MC simulations in chest CT

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Yogesh Thakur

Assistant Professor Department of Radiology University of British Columbia Canada

: J Diagn Tech Biomed Anal

Abstract

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CT examinations are identified as the largest radiation dose/exam contributor to the population from medical imaging. The AAPM report 204 advocated the use of Size Specific Dose Estimates (SSDEs) to dose estimation; however effective dose calculation using SSDE has not been validated. This work aims to determine whether the published k-factor for chest CT is valid using SSDE approach. 24 patients underwent clinically indicated chest CT exams, scanned with our institutional CT protocol. Patient data was categorized into 4 groups based on sex and BMI (large: >25 kg/m2 and small: <25 kg/m2). Monte Carlo (MC) simulations were performed using patient data to estimate organ absorbed dose and calculate E via ICRP-103 methods (E-MC) and compared with E estimated with k-factor (E-k) and with SSDE/k-factor (E-SSDE). A significant difference was found between E-MC and E-k for small females (P<0.05). Differences in E-SSDE and MC-E were significantly different for all groups (P<0.05) except small females, where the difference between E-SSDE and E-MC was not significantly different (P>0.05). The range of difference between E-MC and E-k was +/- 0.8 mSv. Dose was underestimated by 45% for the smallest female (BMI-17.0). Data suggested that E-k is valid to estimate effective dose in chest CT for males between 17-32 BMI and females between 26-30 BMI. Small females were significantly underestimated using the E-k method by upto 45%. SSDE improved E estimates for small females. Use of the currently established k-factor of 0.014 mSv/(mGy-cm) is a valid method to estimate effective dose for males and large females in chest CT.

Biography

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Yogesh Thakur completed his PhD at The University of Western Ontario in 2009. He is currently the Medical Physics Lead at Vancouver Coastal Health Authority and a Clinical Assistant Professor in the Department of Radiology at the University of British Columbia. He has published more than 15 papers in reputed journals, 1 book chapter, and peer reviewed manuscripts for numerous reputed journals. He is a member of the Canadian College of Physicists in Medicine, certified in Diagnostic Imaging and Mammography.

E-Mail: yogesh.thakur@vch.ca