Revealing the radiation dose impact of topogram, and contrast material monitoring scans in paediatric chest CT scans: comparison to adults and establishment of local DRLs

Although the radiation dose impact of planning scans prior to the actual computed tomography (CT) scan has been addressed in previous studies, their systematic assessment across paediatric age groups and their relevance for establishing local diagnostic reference levels (DRLs) have not been thoroughly investigated and are not currently included in guideline recommendations. To investigate the influence of radiation dose from topogram, pre-monitoring, and monitoring scans by age on total radiation exposure and whether their doses need to be considered in DRLs and to establish local DRLs for these scan components. 102 chest CT scans with contrast material monitoring from 101 children (median age 12 years, interquartile range (IQR) 7-16 years) and 4498 chest CT scans from 4476 adults (⩾18 years) between January 2021 and May 2023 were retrospectively analysed. Paediatric scans were grouped into 5 age groups and compared with adult scans. The dose-length product (DLP) of topogram, pre-monitoring, and monitoring scans were evaluated and their effect on total radiation dose was analysed. Local DRLs were established for 5 different age groups. Radiation dose proportions of planning scans to total DLP in chest CT increased with decreasing age group (mainly<i>p</i>< 0.05), with the monitoring scan having the greatest impact. The median topogram proportion increased from 0.3% (⩾18 years) to 1.6% (<1 year), the pre-monitoring proportion from 0.5% (⩾18 years) to 3.5% (<1 year), and the monitoring proportion from 2.2% (⩾18 years) to 26.9% (<1 year). In children under 10 years, monitoring scans in chest CT have a large impact on radiation dose, contributing a median of 13%-27% of the total radiation dose compared to adults (median: 2.2%). Therefore, these planning scans should be monitored and included in radiation dose optimization efforts such as DRLs.