Determination of Diagnostic Reference Level (DRL) in Common Computed Tomography Examinations with the Modified Quality Control-Based Dose Survey Method in Four University Centers: A Comparison of Methods

BACKGROUND: The diagnostic reference level (DRL) is measured with different methods in the common Computed tomography (CT) exams, but it has not been measured through the size-specific dose estimate (SSDE) method in Iran, yet. OBJECTIVE: This study aimed to calculate the local DRL (LDRL) using the new quality control-based dose survey method (QC) and patients’ effective diameter (MQC) and compare them with a data collection method (DC) as well as local national DRLs (NDRL). MATERIAL AND METHODS: In this cross-sectional study, LDRL, based on the third quartile of volumetric computed tomography dose index (CTDI(vol)) and dose length product (DLP) values, was calculated for the four common CT examinations in four CT scan centers affiliated with Shiraz University of Medical Sciences by DC, QC and MQC methods. The CTDI(vol) of each patient for each CT exam calculated with three methods was compared with paired t-test. Also, the LDRL using MQC method was compared with other national DRL studies. RESULTS: There was a significant difference between the CTDI(vol) values calculated with MQC and QC in all four examinations (P <0.001). The LDRL based on CTDI(vol) obtained by the MQC method for head, sinus, chest, abdomen, and pelvis were (50, 18, 15, 19) mGy, respectively, and the calculated DLP values were also (735, 232, 519, 984) mGy.cm. CONCLUSION: In MQC, LDRL based on CTDI(vol) was calculated with a mean difference percentage of (19.2 ± 11.6)% and (27.1 ± 8.1)% as compared to the QC and DC methods, respectively. This difference resulted from the use of the SSDE method and dose accuracy in the QC dose survey