[ Introduction ] :The dosimetric calculations in CT examinations are currently based on two quantities 1),2) . 1.
Volume weighted CT dose Index (CTDI vol ) 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 CTDI vol and DLP,
Methods and Materials
[Methodsand Materials] :The measurement of volume CT dose index (CTDI 100 ) 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.
CTDI vol was calculated (See Appendix 1.1 to 1.4). :The measurement parameters were kept constant: tube voltage,
tube rotation time,
radiation profile width...
[Results] :The relationship between tube current and CTDI vol was shown by the following equation (See Slide No.8). Large focus : CTDI vol = 0.0756 × tube current + 0.7424 Small focus : CTDI vol = 0.0774 × tube current + 0.1189 (In the measurement of CTDI 100, the coefficient of variation was within 5 %.) :The relationship between tube current and DLP 0 was also shown by the following equation (See Slide No.9). DLP 0 = 0.459 × tube current (average current value of first and last images for...
: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] 1) Size-specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations AAPM Report No.204 2) Cynthia H.
Shuai Leng ,
Lifeng Yu and et al CT Dose Index and Patient Dose :They Are Notthe Same Thing Radiology,
(2011) 3) A.
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...