ABSTRACT
PURPOSE: The purpose of this study was to develop a gantry overrun corrected CTDIvol (cCTDIvol) dosimetry and evaluate the differences between the displayed CTDIvol (dCTDIvol), measured CTDIvol (mCTDIvol), and the cCTDIvol. METHODS AND MATERIALS: The each 8 rotation times between 275 and 1000ms of two CT scanners were investigated. Rotation time (Trot) and the beam-on time (Tbeam) in axial scanning were measured accurately to determine the gantry overrun time (Tover) as Tbeam-Trot. Subsequently, mCTDIvol was measured by using a 100mm ionization chamber and CTDI phantoms. Furthermore, we introduced a gantry overrun correction factor (Co=Trot/Tbeam) to obtain cCTDIvol. Upon completion of the data acquisition, the dCTDIvol and mCTDIvol were compared with the cCTDIvol. RESULTS: The discrepancies of Trot were 0.2±0.2ms as compared to the preset rotation times, and Tover was machine-specific and almost constant (22.4±0.5ms or 45.1±0.3ms) irrespective of the preset rotation time. Both dCTDIvol and mCTDIvol were increasingly overestimated compared to cCTDIvol as the faster the preset rotation time was selected (1.7-23.5%). CONCLUSION: The rotation time influences the accuracy of CTDIvol in modern CT, and should be taken into consideration when assessing the radiation output in modern CT.
