Document Type : Original Paper
Department of Radiology and Radiotherapy Technology, International Campus, Tehran University of Medical Sciences, Tehran, Iran.
Department of Radiology and Radiotherapy Technology, School of Allied Medical Sciences, Tehran University of Medical Sciences, Tehran, Iran.
Introduction: The rapid use of computed tomography (CT) scan is of great concern, due to increase in patients’ dose. Optimization of CT protocol is a vital issue in dose reduction. This study aimed to optimize radiation dose in cranial CT and assess modifications in image quality under radiation dose reduction.
Material and Methods: A poly(methyl methacrylate) phantom was used for quality control test on CT scanners. Data of 214 scan parameters, dose indicators; volume CT dose index (CTDIvol) and dose-length product (DLP) of patients who underwent cranial CT scans were collected. The data were grouped into three, with respect to the slice numbers of 24, 28, and 32. Tube voltage (kVp) and slice thickness were constant; (110 kVp and 4.8 mm, respectively), at variable tube currents (mAs). A one-sample t-test was used to compare the dose indicator values of the hospital protocol with a recommended protocol. Scan parameters were optimized for radiation dose against image quality.
Results: Increased mAs resulted in increased CTDIvol and DLP at constant kVp and slice thickness. Moreover, dose indicators recorded the lowest and highest values at the slice numbers of 24 and 32, respectively. An increase in slice numbers affected dose indicators. Dose indicators recorded significant reduction (p <0.001) in comparison to the recommended protocol.
Conclusion: Optimization of CT protocol considers radiation dose and image quality. Radiologists adopted protocols acquired with lower scan parameters and dose indicators lower than the recommended achievable dose limit of 58 mGy.