Determination of dose delivery accuracy in CT examinations

Volume computed tomography dose index (CTDIvol) represents an average dose within a scan volume for a standardized CTDI phantom. It is a useful indicator of the dose to the standardized phantom for a specific examination protocol. Dose index (CTDIvol) for head and body PMMA phantoms have been estimated in this study and comparison made with corresponding console displayed doses. The study was performed on 40 slice CT system, and measurements were done with 100 mm long pencil ion chamber connected to an electrometer. Doses were estimated using the AAPM Report 96 formalism. Estimated dose for head scan technique (120 kV, 150 mAs) was 44.30 mGy, deviating from the console displayed dose by 4.49%. The body (pelvic) scan technique of 120 kV and 100 mAs produced a dose estimate of 20.08 mGy in the body phantom, deviating by 3.05% from the console displayed dose. The estimated head and body phantom doses were compared to selected international dose reference levels and varying deviations were observed.