Size-specific dose estimates for pediatric head CT protocols based on the AAPM report TG-293

To establish the Size Specific Dose Estimate (SSDE) typical values for pediatric head CT examinations based on the AAPM report TG-293; to provide a new stratification based on the water-equivalent diameter (D_w), given that SSDE is related to the head size.

296 Head CT scans of pediatric patients collected using a dose monitoring software were retrospectively analysed. Typical values were derived stratifying data by age in three methods: the first proposed by the European Guidelines on Diagnostic Reference Levels for Pediatric Imaging (RP185), the second by the National Istisan Report 20/22 and a local one related to the clinical protocols (LStrata). For each scan, a self-developed Matlab routine calculated the water-equivalent diameter (D_w) and related SSDE values with the conversion factors f^H16and f^B16provided by the AAPM reports TG-293 and TG-204, respectively. Eventually, a D_wstratification was introduced starting from a measure of the lateral dimension of the head.

SSDE based on TG-204 overestimatesthe dose up to 12%. Four D_wgroups were identified thanks to the good correlation between the head lateral dimension andD_w: D_w < 14 cm, 14 ≤ D_w < 16 cm, 16 ≤ D_w< 17 cm, D_w≥ 17 cm. The D_w-stratified dosimetric indices presentgreater variability than those grouped by age because of the large variability of the size of the infant's head.

The variability of the SSDE metric underlines that age-optimized protocols are not when size is considered.