National diagnostic reference levels (NDRLs) of Iran were determined for the four most common CT examinations including head, sinus, chest and abdomen/pelvis. A new 'quality control (QC)-based dose survey method', as developed by us, was applied to 157 CT scanners in Iran (2014-15) with different slice classes, models and geographic spread across the country. The NDRLs for head, sinus, chest and abdomen/pelvis examinations are 58, 29, 12 and 14 mGy for CTDIVol and 750, 300, 300 and 650 mGy.cm for DLP, respectively. The 'QC-based dose survey method' was further proven that it is a simple, accurate and practical method for a time and cost-effective NDRLs determination. One effective approach for optimization of the CT examination protocols at the national level is the provision of an adequate standardized training of the radiologists, technicians and medical physicists on the patient radiation protection principles and implementation of the DRL concept in clinical practices.
The practical aspects of two recently developed patient dose optimization methods in computed tomography (CT) examinations, size-specific dose estimate (SSDE) and acceptable quality dose (AQD), were verified for the chest and abdomen/pelvis examinations. A dose survey was performed in a CT institute by considering patients lateral diameter, weight and body mass index (BMI). The AQD tables for weight and BMI groups and SSDE threshold curves were obtained. The mean of volume CT dose index and dose length product for standard-size patients were compared with the national diagnostic reference levels (NDRLs) of Iran. The results show that patient doses are below the NDRLs. It is more reliable to report the AQDs based on SSDE and for BMI groups which can well take into account patient size in the dose optimization process. The SSDE threshold curves can be determined with more precision by including dose data of all possible sizes in the curves.
A new "quality-control-based (QC-based) dose survey method" has been developed for determination of diagnostic reference levels (DRL) in Computed Tomography (CT) examinations. The "QC-based dose survey method" is based on the use of retrospective data in the QC documents and reports, which are typically available from the National Regulatory Authority database. The method was applied to 70 CT scanners in Tehran, Iran, by using the available QC reports from the database. The commonly used "data collection method" was also applied by filling each questionnaire on-site to validate the new method. Using the new QC-based and data collection methods, the DRLs of four common CT examinations: head, sinus, chest, and abdomen/pelvis were determined and compared. The DRLs determined by the "QC-based method" for head, sinus, chest, and abdomen/pelvis are 59, 29, 10, and 13 mGy, respectively, for the volume computed tomography dose index (CTDIVol) and 834, 235, 233, and 522 mGy-cm for the dose length product (DLP), respectively. The difference between the DRLs obtained by the two methods is on the average 6.7 ± 5.7%, which is within the acceptance tolerance level of the IAEA for QC dosimetry tests. The "QC-based dose survey method" is believed to be an effective alternative method to the other commonly used "data collection" and "direct dose measurement method" for determination of CT examination DRLs. This new method has unique characteristics such as simplicity, time and cost effectiveness, highly reduced clinical interruptions and collaborations, and potential for large-scale surveys with capability for more frequent review of national DRL values.
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%).
The purpose of this study was to evaluate the effects of the gantry angulation on dose profiles along the z-axis, the CTDIW value and the CTDIW efficiency in the head examinations. A Monte Carlo simulation model of a GE LightSpeed 16-slice CT scanner was developed by a GATE toolkit. The CTDI100 in air at the isocenter and in a head dosimetry phantom were measured using a pencil ion chamber. Dose profiles were studied in the central and peripheral holes of the head phantom using thermoluminescence LiF disc dosemeters for gantry angulations of 0°, 10° and 20°. Results show a small shift for only the peripheral dose profiles with increasing the gantry angulation (maximum shift of 24 mm at 20°). The peak amplitude of the dose profiles was reduced for both of the central and peripheral holes by ~5%, while the CTDIW values and the CTDIW efficiencies did not change significantly.
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