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

Abstract

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.

Applying the AAPM 293 report to estimate the absorbed dose during head computed tomography: using head circumference for rapid dose estimation

“…CTDI vol and DLP indicate the absorbed dose of polymethyl methacrylate (PMMA) phantoms with defined diameters of 16 and 32 cm for the head and body, respectively ( 6 - 9 ). However, CTDI vol and DLP do not represent the actual absorbed patient dose, as they do not account for patient size ( 10 , 11 ). The American Association of Physicists in Medicine (AAPM) aimed to improve the accuracy of patient dose estimation by proposing a formula to calculate the size-specific dose estimate (SSDE) ( 12 , 13 ), and in 2019 issued report 293 to estimate the dose for head CT examinations ( 14 ).…”