Purpose
[ Introduction ]
:The dosimetric calculations in CT examinations are currently based on two quantities1),2).
1.
Volume weighted CT dose Index (CTDIvol)
2.
Dose-length product (DLP)
:These quantities during each examination can be obtained from the displayed values on CT scanner console.
But the calculation methods of these quantities are different between each CT facilities.
In TOSHIBA medical system uses maximum value and mean value for calculating the CTDIvol and DLP,
respectively,
in the scan length during examination.
But the details of these methods are...
Methods and Materials
[Methodsand Materials]
:The measurement of volume CT dose index (CTDI100) was carried out using 64-row multidetector CT (TOSHIBA Medical Systems),
a pencil ion chamber,
and a polymethyl methacrylate phantom with a diameter of 32 cm (See Slide No.1 and 2).
:From the central and peripheral values,
a weighted CTDI was calculated.
Then,
CTDIvol was calculated (See Appendix 1.1 to 1.4).
:The measurement parameters were kept constant: tube voltage,
tube rotation time,
radiation profile width (RPW) ,
beam pitch,
and scan FOV were 120 kV,
0.5...
Results
[Results]
:The relationship between tube current and CTDIvol was shown by the following equation (See Slide No.8).
Large focus : CTDIvol = 0.0756 × tube current + 0.7424
Small focus : CTDIvol = 0.0774 × tube current + 0.1189
(In the measurement of CTDI100,the coefficient of variation was within 5 %.)
:The relationship between tube current and DLP0 was also shown by the following equation (See Slide No.9).
DLP0 = 0.459 × tube current (average current value of first and last images for each scan)...
Conclusion
:The displayed and calculated DLP during chest CT examinations were in good agreement.
:This software is useful tool for estimating DLP of chest CT examinations with tube current modulation techniques.
References
[References]
1)Size-specific Dose Estimates (SSDE) in Pediatric and Adult Body CT
Examinations
AAPM Report No.204
2) Cynthia H.
McCollough ,
Shuai Leng ,
Lifeng Yu and et al
CT Dose Index and Patient Dose :They Are Notthe Same Thing
Radiology,
259,
(2011)
3) A.
Tzedakis,
J.
Damilakis,
K.
Perisinakis,
and et al
The effect of z overscanning on patient effective dose from
multidetector helical computed tomography examinations
Med Phys 32 ,
(2005)
4) A TSALAFOUTAS ,
S I METALLIDIS and et al
A method for...