Investigation and analysis of CT doses to examined individuals in Henan province

Objective To study the level of doses which children and adults received from CT examinations in Henan province, and to explore the influencing factors, so as to provide basic data for the development of diagnostic reference (guidance) level for CT examination in China and related regions. Methods A total of 1 113 subjects, which have received examinations by 31 CT scanners separately in 7 cities of the province, were selected using stratified quota sampling method to carry out the dose survey, including basic information on subjects, equipment, scanning parameters, and dosimetry, etc. Typical effective dose was estimated by using dose conversion coefficient. Results In the conventional CT scanning of head. The 75% of CTDIw for children aged 0-1, >1-5, >5-10 and >10-15 years were 32.2, 37.2, 43.0 and 46.7 mGy; 75% of DLP were 478.0, 572.0, 715.6 and 743.9 mGy·cm and effective doses were 5.26, 3.83, 2.86 and 2.38 mSv, respectively. In the routine chest scanning, 75% of CTDIw for children aged 0-1, >1-5, >5-10 and >10-15 years were all 9.3 mGy. The 75% of DLP were 141.7, 178.8, 224.0 and 238.7 mGy·cm; and effective doses were 5.53, 4.64 4.03 and 3.10 mSv, respectively. 75% of CTDIw for head, chest and abdomen of the adult subjects from CT examinations were 57.4, 16.2 and 19.4 mGy, respectively. The 75% of DLP were 818.3, 504.7 and 571.1 mGy·cm, respectively, and effective doses were 1.72, 7.07 and 8.57 mSv, respectively. Conclusions As the update of CT equipment, increasing progress in examination technology and rapid increase in CT application frequency, medical institutions should choose the scanning parameters with respect to various types of CT scanner to optimize the image quality and the radiation doses. The diagnostic reference level for CT examination should be improved, especially for children. Key words: CT; CT dose index; Dose length product; Effective dose; Diagnostic reference level