Diagnostic Reference Levels for Computed Tomography Examinations in Iran: A Nationwide Radiation Dose Survey

Introduction: International Commission on Radiological Protection introduced three basic principles of radiation protection, namely justification, optimization, and dose limit. Medical exposure has no dose limits, and generally, diagnostic reference levels are used as a tool for optimization of patient protection. Material and Methods: Dosimetry was performed on 20 CT scanners located in 14 cities in 12 provinces of Iran. A calibrated pencil-shaped ionization chamber, standard head and body CT dosimetry phantoms and a radiation monitor were used to determine and calculate Computed Tomography Dose Index (CTDI) and Dose Length Product (DLP). The DLP-based estimates of effective dose were derived using effective dose conversion coefficients. Results: The nCTDIw values for head phantoms fell within the range of 22.05-168.38 and 43.77-426.69 µGy/mAs for 5 and 10mm slice thicknesses, respectively. These values for body phantom were 4.65-146.39 and 9.43-308.92 µGy/mAs for 5 and 10mm slice thicknesses, respectively. The third quartile of CTDIvol and DLP values for head CT examinations were 49.85 mGy and 1161.00 mGy-cm, respectively. The body CT examinations had the values of 8.89 mGy and 370.97 mGy-cm, respectively. The findings of this study revealed that the above-mentioned values can be considered as national diagnostic reference levels for head and body CT examinations in Iran. Conclusion: The results of the current study suggested that there is a need to re-assess DRLs for CT examinations at regular time intervals by the appropriate regulatory authority which can improve the continuous performance of CT scanners in Iran.