PMID- 23127050
OWN - NLM
STAT- MEDLINE
DCOM- 20130114
LR  - 20220311
IS  - 0094-2405 (Print)
IS  - 0094-2405 (Electronic)
IS  - 0094-2405 (Linking)
VI  - 39
IP  - 11
DP  - 2012 Nov
TI  - Effects of protocol and obesity on dose conversion factors in adult body CT.
PG  - 6550-71
LID - 10.1118/1.4754584 [doi]
AB  - PURPOSE: In computed tomography (CT), organ dose, effective dose, and risk index 
      can be estimated from volume-weighted CT dose index (CTDI(vol)) or dose-length 
      product (DLP) using conversion coefficients. Studies have investigated how these 
      coefficients vary across scanner models, scan parameters, and patient size. 
      However, their variability across CT protocols has not been systematically 
      studied. Furthermore, earlier studies of the effect of patient size have not 
      included obese individuals, which currently represent more than one-third of U.S. 
      adults. The purpose of this study was to assess the effects of protocol and 
      obesity on dose and risk conversion coefficients in adult body CT. METHODS: 
      Whole-body computational phantoms were created from clinical CT images of six 
      adult patients (three males, three females), representing normal-weight patients 
      and patients of three obesity classes. Body CT protocols at our institution were 
      selected and categorized into ten examination categories based on anatomical 
      region examined. A validated Monte Carlo program was used to estimate organ dose. 
      Organ dose estimates were normalized by CTDI(vol) and size-specific dose estimate 
      (SSDE) to obtain organ dose conversion coefficients (denoted as h and h(ss) 
      factors, respectively). Assuming each phantom to be 20, 40, and 60 years old, 
      effective dose and risk index were calculated and normalized by DLP to obtain 
      effective dose and risk index conversion coefficients (denoted as k and q 
      factors, respectively). Coefficient of variation was used to quantify the 
      variability of each conversion coefficient across examination categories. The 
      effect of obesity was assessed by comparing each obese phantom with the 
      normal-weight phantom of the same gender. RESULTS: For a given organ, the 
      variability of h factor across examination categories that encompassed the entire 
      organ volume was generally within 15%. However, k factor varied more across 
      examination categories (15%-27%). For all three ages, the variability of q factor 
      was small for male (<10%), but large for female phantoms (21%-43%). Relative to 
      the normal-weight phantoms, the reduction in h factor (an average across fully 
      encompassed organs) was 17%-42%, 17%-40%, and 51%-63% for obese-class-I, 
      obese-class-II, and obese-class-III phantoms, respectively. h(ss) factor was not 
      independent of patient diameter and generally decreased with increasing obesity. 
      Relative to the normal-weight phantoms, the reduction in k factor was 12%-40%, 
      14%-46%, and 44%-59% for obese-class-I, obese-class-II, and obese-class-III 
      phantoms, respectively. The respective reduction in q factor was 11%-36%, 
      17%-42%, and 48%-59% at 20 years of age and similar at other ages. CONCLUSIONS: 
      In adult body CT, dose to an organ fully encompassed by the primary radiation 
      beam can be estimated from CTDI(vol) using a protocol-independent conversion 
      coefficient. However, fully encompassed organs only account for 50% +/- 19% of k 
      factor and 46% +/- 24% of q factor. Dose received by partially encompassed organs 
      is also substantial. To estimate effective dose and risk index from DLP, it is 
      necessary to use conversion coefficients specific to the anatomical region 
      examined. Obesity has a significant effect on dose and risk conversion 
      coefficients, which cannot be predicted using body diameter alone. 
      SSDE-normalized organ dose is not independent of diameter. SSDE itself generally 
      overestimates organ dose for obese patients.
FAU - Li, Xiang
AU  - Li X
AD  - Department of Radiology, Duke University Medical Center, Durham, NC 27705, USA.
FAU - Samei, Ehsan
AU  - Samei E
FAU - Williams, Cameron H
AU  - Williams CH
FAU - Segars, W Paul
AU  - Segars WP
FAU - Tward, Daniel J
AU  - Tward DJ
FAU - Miller, Michael I
AU  - Miller MI
FAU - Ratnanather, J Tilak
AU  - Ratnanather JT
FAU - Paulson, Erik K
AU  - Paulson EK
FAU - Frush, Donald P
AU  - Frush DP
LA  - eng
GR  - R01 EB001838/EB/NIBIB NIH HHS/United States
GR  - R01EB001838-06/EB/NIBIB NIH HHS/United States
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PT  - Research Support, Non-U.S. Gov't
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
SB  - IM
MH  - Adult
MH  - Female
MH  - Humans
MH  - Male
MH  - Middle Aged
MH  - Monte Carlo Method
MH  - Neoplasms, Radiation-Induced/etiology
MH  - *Obesity
MH  - Phantoms, Imaging
MH  - *Radiation Dosage
MH  - Radiometry
MH  - Risk
MH  - Tomography, X-Ray Computed/adverse effects/*methods
MH  - Whole-Body Irradiation
PMC - PMC3482255
EDAT- 2012/11/07 06:00
MHDA- 2013/01/15 06:00
PMCR- 2013/11/01
CRDT- 2012/11/07 06:00
PHST- 2012/11/07 06:00 [entrez]
PHST- 2012/11/07 06:00 [pubmed]
PHST- 2013/01/15 06:00 [medline]
PHST- 2013/11/01 00:00 [pmc-release]
AID - 052210MPH [pii]
AID - 10.1118/1.4754584 [doi]
PST - ppublish
SO  - Med Phys. 2012 Nov;39(11):6550-71. doi: 10.1118/1.4754584.