PMID- 27806599
OWN - NLM
STAT- MEDLINE
DCOM- 20170315
LR  - 20170315
IS  - 2473-4209 (Electronic)
IS  - 0094-2405 (Linking)
VI  - 43
IP  - 11
DP  - 2016 Nov
TI  - A study of the midpoint dose to CTDI(vol) ratio: Implications for CT dose 
      evaluation.
PG  - 5878
AB  - PURPOSE: In multidetector CT, the volume CT dose index (CTDI(vol)) is reported 
      for each scan series and dose conversion factors are used for the size-specific 
      dose estimate (SSDE) and scanner-independent organ dose evaluation. This study 
      aimed at examining the dependencies of conversion factors on scan length, tube 
      voltage, and subject size. The results may be insightful for evaluating the dose 
      from CT examinations with large variations in patient size and scan length. 
      METHODS: A previously developed Monte Carlo simulation program was used to 
      simulate single rotation axial scans of two standard CTDI phantoms [material 
      polymethyl methacrylate (PMMA), diameters 16 and 32 cm] and multiple water 
      cylinders at five tube voltages (70, 80, 100, 120, and 140 kV). The resultant 
      longitudinal dose profiles were used to calculate CTDI(L)(water)/CTDI(w) (PMMA), 
      where L was dose integration length. The ratio was equal to the midpoint dose 
      D(L)(0) (water) to CTDI(vol) ratio in a CT scan series with a scan length equal 
      to L. RESULTS: For water phantom diameters from 11 to 50 cm and scan lengths from 
      15 to 30 cm, the changes of D(L)(0)/CTDI(vol) from that of 120 kV and 20-cm scan 
      length were between -18.4% and 11.7%. This was consistent with the CTDI(vol) to 
      SSDE conversion factors of AAPM Report No. 204. For scan lengths less than 15 cm, 
      D(L)(0)/CTDI(vol) decreased considerably as L decreased. D(L)(0)/CTDI(vol) was 
      shown to be 17.3%-31.4% lower for L = 5 cm than for L = 15 cm, when the tube 
      voltage was 120 kV and phantom diameter ranged from 11 to 50 cm. As tube voltage 
      increased from 80 to 140 kV, D(L)(0)/CTDI(vol) decreased at small diameters while 
      it increased at large diameters. The change was 9.4% with a diameter of 18 cm and 
      a scan length of 20 cm and 17.6% with a diameter of 40 cm and a scan length of 30 
      cm. CONCLUSIONS: The midpoint dose to CTDI(vol) ratio varies widely across the 
      clinical scan lengths from a few millimeters to about 1 m and varies moderately 
      across tube voltages from 70 to 140 kV. The comprehensive data provided in the 
      Appendix can be used for assessing the dose from short-length scans and improving 
      the dose evaluation in CT.
FAU - Li, Xinhua
AU  - Li X
AD  - Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts 
      General Hospital, Boston, Massachusetts 02114.
FAU - Yang, Kai
AU  - Yang K
AD  - Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts 
      General Hospital, Boston, Massachusetts 02114.
FAU - Liu, Bob
AU  - Liu B
AD  - Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts 
      General Hospital, Boston, Massachusetts 02114.
LA  - eng
PT  - Journal Article
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
SB  - IM
MH  - Monte Carlo Method
MH  - Phantoms, Imaging
MH  - *Radiation Dosage
MH  - Radiometry
MH  - Tomography, X-Ray Computed/instrumentation/*methods
EDAT- 2016/11/04 06:00
MHDA- 2017/03/16 06:00
CRDT- 2016/11/04 06:00
PHST- 2016/11/04 06:00 [pubmed]
PHST- 2017/03/16 06:00 [medline]
PHST- 2016/11/04 06:00 [entrez]
AID - 10.1118/1.4963811 [doi]
PST - ppublish
SO  - Med Phys. 2016 Nov;43(11):5878. doi: 10.1118/1.4963811.