Fig. 4

Distribution of total dose-length product (DLP) and volumetric computed tomography dose index (CTDI_vol) for study common name (SCN) “CT Head WO” and comparison with values from ISTISAN 17/33 [18]. The median value and range between 25th and 75th percentile are shown in black dashed lines; the red dashed line reports the diagnostic reference level (DRL) provided by ISTISAN 17/33 [18]. The narrow shape of CTDIvol histogram points out similar values among scanners and highlights the use of fixed mAs values. The DLP histogram shows several peaks. On the one hand, the anatomical region was very similar from one patient to another; on the other hand, the scanners used different collimations, and therefore, the entire anatomical range is covered by a fixed and scanner-dependent number of acquisitions (axial mode). The final peak, more or less evident in all distributions (see the following Figs. 5, 6, 7, 8, and 9), is caused by the inclusion in the last class of values higher than the considered range