PMID- 28681439
OWN - NLM
STAT- MEDLINE
DCOM- 20180523
LR  - 20180523
IS  - 2473-4209 (Electronic)
IS  - 0094-2405 (Linking)
VI  - 44
IP  - 10
DP  - 2017 Oct
TI  - Characterization of radiation dose from tube current modulated CT examinations 
      with considerations of both patient size and variable tube current.
PG  - 5413-5422
LID - 10.1002/mp.12460 [doi]
AB  - PURPOSE: The volume CT dose index (CTDI(vol) ) and the size-specific dose 
      estimate (SSDE) are widely used for monitoring patient dose from CT examinations. 
      Both metrics may represent the average dose over the central scan plane of the 
      CTDI phantom or the patient under constant tube current (mA), but they are not 
      intended for the tube current modulation (TCM)-enabled CT examinations, in which 
      the peak dose across the scanned range may not be at the scan range center. To 
      overcome the limitation, this paper illustrates an alternative approach, its 
      implementation, and the relationship between longitudinal dose distribution D(L) 
      (z) in water cylinder and mA line shape, scan length, as well as phantom 
      diameter. METHODS: A dose calculation algorithm and the published data by Li 
      et al. [Med. Phys. 40, 031903 (10pp.) (2013); 41, 111910 (5pp.) (2014)] were used 
      to calculate D(L) (z) for the central and peripheral axes of 10- to 50-cm 
      diameter water phantoms undergoing CT scans of one constant and three variable mA 
      distributions, each of which in three scan lengths of 10, 28.6, and 50 cm. All 
      scans had an identical average tube current over the scan ranges. The results in 
      the scanned ranges were used to assess the D(L) (z) to mA(z) ratios, and their 
      coefficients of variation (CV = stdev/mean) were used to compare the line shapes 
      of D(L) (z) and mA(z) for congruence: identical line shapes would result in 
      CV = 0, but largely different line shapes would result in high CV. RESULTS: In 
      30-cm diameter water phantom, the line shape of D(L) (z) was largely different 
      from that of mA(z). CV was higher in a variable mA scan than in a constant mA 
      scan. As the scan length of variable mA scan increased, CV mostly decreased, and 
      the line shape of D(L) (z) more closely resembled that of mA(z). When two phantom 
      axes were compared, CV was smaller and the line shape of D(L) (z) more closely 
      resembled that of mA(z) on the peripheral axis than on the central axis. In 41 
      water phantoms included in this study, CV mostly increased with phantom diameter, 
      and approached the limiting levels on the peripheral axes of large phantoms. In 
      constant mA scans, CV ranged from 5.5% to 14.0% on the phantom central axes and 
      from 4.6% to 6.4% on the phantom peripheral axes. However, in variable tube 
      current scans, CV ranged from 7.4% to 70.0% on the phantom central axes and from 
      5.1% to 35.9% on the phantom peripheral axes. CONCLUSION: D(L) (z) (water) may be 
      advantageous over current CT dose metrics in characterizing the dose dependences 
      on both patient size and mA line shape from tube current modulated examinations. 
      Evaluating D(L) (z) (water) with the water equivalent diameter and tube current 
      curve from clinical examinations has a potential to improve CT dose monitoring 
      program.
CI  - (c) 2017 American Association of Physicists in Medicine.
FAU - Li, Xinhua
AU  - Li X
AD  - Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts 
      General Hospital, Boston, MA, 02114, USA.
FAU - Yang, Kai
AU  - Yang K
AD  - Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts 
      General Hospital, Boston, MA, 02114, USA.
FAU - Liu, Bob
AU  - Liu B
AD  - Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts 
      General Hospital, Boston, MA, 02114, USA.
LA  - eng
PT  - Journal Article
DEP - 20170802
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
SB  - IM
MH  - Algorithms
MH  - *Body Size
MH  - Humans
MH  - Phantoms, Imaging
MH  - *Radiation Dosage
MH  - Tomography, X-Ray Computed/instrumentation/*methods
OTO - NOTNLM
OT  - characterization
OT  - computed tomography (CT)
OT  - patient size
OT  - radiation dose
OT  - tube current modulation
EDAT- 2017/07/07 06:00
MHDA- 2018/05/24 06:00
CRDT- 2017/07/07 06:00
PHST- 2016/10/01 00:00 [received]
PHST- 2017/06/25 00:00 [revised]
PHST- 2017/06/28 00:00 [accepted]
PHST- 2017/07/07 06:00 [pubmed]
PHST- 2018/05/24 06:00 [medline]
PHST- 2017/07/07 06:00 [entrez]
AID - 10.1002/mp.12460 [doi]
PST - ppublish
SO  - Med Phys. 2017 Oct;44(10):5413-5422. doi: 10.1002/mp.12460. Epub 2017 Aug 2.