A New Dual-purpose Quality Control Dosimetry Protocol for Diagnostic Reference-level Determination in Computed Tomography

Abstract

A diagnostic reference level is an advisory dose level set by a regulatory authority in a country as an efficient criterion for protection of patients from unwanted medical exposure. In computed tomography, the direct dose measurement and data collection methods are commonly applied for determination of diagnostic reference levels. Recently, a new quality-control-based dose survey method was proposed by the authors to simplify the diagnostic reference-level determination using a retrospective quality control database usually available at a regulatory authority in a country. In line with such a development, a prospective dual-purpose quality control dosimetry protocol is proposed for determination of diagnostic reference levels in a country, which can be simply applied by quality control service providers. This new proposed method was applied to five computed tomography scanners in Shiraz, Iran, and diagnostic reference levels for head, abdomen/pelvis, sinus, chest, and lumbar spine examinations were determined. The results were compared to those obtained by the data collection and quality-control-based dose survey methods, carried out in parallel in this study, and were found to agree well within approximately 6%. This is highly acceptable for quality-control-based methods according to International Atomic Energy Agency tolerance levels (±20%).

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

“…All these differences in calculating LDRL and NDRL by QC methods in comparison to this study could be attributed to the scan pa- Deevband et al [22] and Sohrabi et al [23]. The year mentioned in the table for each study is the study year, and the numbers in parentheses show the number of computed tomography (CT) scanners in each study.…”

“…If we add the patient effective diameter to the cause of the difference in the calculated CT-DI vol and the scan parameters in QC method respected to DC method, reflected more in the chest and abdomen/pelvis examinations, it reveals the cause of the statistically significant difference between MQC and QC method in each examination (P<0.001). Also, the DRL calculated based on CTDI vol and DLP for four examinations was higher than (except for sinus) all studies conducted with QC method [11,23] and NDRL studies with the QC and DC methods [18,21] (Table 4 and Figure 4). The decrease in the sinus examination dose in studies using QC (2, 3) and dual-purpose QC methods [23] is not particularly linked to the patient size and it may be originated from the low values of the mAs in this examination, also in the present study (Table 1).…”

“…Also, the DRL calculated based on CTDI vol and DLP for four examinations was higher than (except for sinus) all studies conducted with QC method [11,23] and NDRL studies with the QC and DC methods [18,21] (Table 4 and Figure 4). The decrease in the sinus examination dose in studies using QC (2, 3) and dual-purpose QC methods [23] is not particularly linked to the patient size and it may be originated from the low values of the mAs in this examination, also in the present study (Table 1). An American study conducted by Kanal et al [20] is the only study, used the SSDE method to measure NDRL.…”

“…Also, in the present study, the DRL result is closer to the NDRL obtained for CTDI vol with QC than the DC and Di methods used in NDRL study conducted by Najafi et al [18], and Deevband et al [22] studies, respectively. In another study, besides the QC method, the dual purpose quality control method was used for DRL calculation of five CT scanners by changing the QC method in Shiraz, but the centers were not identified [23]. In this method, after calculation of CT-DI vol based on CTDI air and the conversion factor P, the DRL for five CT examinations was calculated through high-precision dosimetry by the QC report parameter, pitch number, and a radiologist's approval of image quality [23].…”

“…In another study, besides the QC method, the dual purpose quality control method was used for DRL calculation of five CT scanners by changing the QC method in Shiraz, but the centers were not identified [23]. In this method, after calculation of CT-DI vol based on CTDI air and the conversion factor P, the DRL for five CT examinations was calculated through high-precision dosimetry by the QC report parameter, pitch number, and a radiologist's approval of image quality [23]. The DRL for CTDI vol in the present study differs with a mean value of 10.3% and 6.6% with the QC and dual-purpose QC methods in the same study, as well as 27.7% and 17% for DLP (Table 4).…”