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An in vitro study of the dose responses of human peripheral blood lymphocytes was conducted with the aim of creating calibrated dose-response curves for biodosimetry measuring up to 4 Gy (0.25-4 Gy) of gamma radiation. The cytokinesis-blocked micronucleus (CBMN) assay was employed to obtain the frequencies of micronuclei (MN) per binucleated cell in blood samples from 16 healthy donors (eight males and eight females) in two age ranges of 20-34 and 35-50 years. The data were used to construct the calibration curves for men and women in two age groups, separately. An increase in micronuclei yield with the dose in a linear-quadratic way was observed in all groups. To verify the applicability of the constructed calibration curve, MN yields were measured in peripheral blood lymphocytes of two real overexposed subjects and three irradiated samples with unknown dose, and the results were compared with dose values obtained from measuring dicentric chromosomes. The comparison of the results obtained by the two techniques indicated a good agreement between dose estimates. The average baseline frequency of MN for the 130 healthy non-exposed donors (77 men and 55 women, 20-60 years old divided into four age groups) ranged from 6 to 21 micronuclei per 1000 binucleated cells. Baseline MN frequencies were higher for women and for the older age group. The results presented in this study point out that the CBMN assay is a reliable, easier and valuable alternative method for biological dosimetry.

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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.

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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.

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