Estimation of cardiac CT angiography radiation dose toward the establishment of national diagnostic reference level for CCTA in Iran

In recent years, with the introduction of 64-slice CT and dual-source CT technology, coronary CT angiography (CCTA) has emerged as a useful diagnostic imaging modality as a non-invasive assessment of coronary heart disease. CT produces a larger radiation dose than other imaging tests and cardiac CT involves higher radiation dose with the advances in the spatial and temporal resolution. The aims of this study are patient dose assessment and establishment of national diagnostic reference level for CCTA in Iran. A questionnaire was sent to CCTA centers. Data for patient and CT protocols were obtained. The volumetric CT dose index (CTDI_vol), dose length product (DLP) and total DLP were considered in the 32 cm standard body phantom. Calculation of estimated effective dose (ED) was obtained by multiplying the DLP by a conversion factor [k = 0.014 mSv (mGy.cm)^-1 ]. Mean value of CTDI_vol and DLP for CCTA was 50 mGy and 825 mGy.cm. The third quartile (75.) of the distribution of mean CTDI-v-o-l (66.54 mGy) and DLP (1073 mGy.cm) values was expressed as the diagnostic reference level (DRL) for CCTA in Iran. The median of ED was 10.26 mSv and inter-quartile range of ED was 7.08-15.03 mSv. A large variety in CTDI_vol and DLP among CT scanner and different sites due to variability in CT parameter is noted. It seems that training could help to reduce patient's dose. (authors)