Preliminary study on the typical values of diagnostic reference level in children′s CT examinations / 中华放射医学与防护杂志

ABSTRACT

Objective:To calculate the typical values of diagnostic reference levels (DRLs) for CT examinations of head, chest and abdomen-pelvis in children using the volumetric CT dose index (CTDI vol), the size-specific dose estimation value (SSDE WD) based on the water equivalent diameter (WD) and the dose length product (DLP) as indicators to measure the radiation dose level of CT examinations in Department of Radiology, Children′s Hospital of Nanjing Medical University. Methods:The CT examination images of patients admitted to the Hospital from January 2021 to December 2021 were retrospectively collected, encompassing 1 391 for head, 1 386 for chest and 1 035 for abdomen-pelvis. Their age, CTDI vol and DLP were recorded and the anterior-posterior diameter (AP), lateral diameter (LAT), area (A ROI) and CT value within area (CT ROI) of the middlemost scanned image were measured manually. The effective diameter ( d), WD, conversion factor ( f16/32X SIZE) and SSDE WD were calculated in accordance with the American Academy of Physicists in Medicine (AAPM) reported method . Patients were divided into 5 groups in terms of their examined site. age and body size <1, 1-, 5-, 10-, and 15- years old. The number of patients in each group was 252, 320, 400, 380 and 39 for the head, 188, 320, 399, 398 and 81 for the chest, and 75, 310, 310, 300 and 40 for the abdomen-pelvis region. The patients for head examination was divided into five groups of <12.5, 12.5-, 14-, 15-, 16-cm based on LAT, with 151, 222, 319, 399 and 300 cases in each group, respectively. The chest and abdomen-pelvis were divided into five groups of <15, 15-, 20-, 25-, 30- cm based on d, with 275, 527, 400, 165 and 19 cases in each chest group, respectively; the abdomen-pelvis 403, 410, 184, 34 and 4 cases. The 75th percentile of CTDI vol, SSDE WDand DLP were counted in each group as typical DRL values, and the differences between CTDI vol and SSDE WD in measuring radiation dose were compared. Results:The typical values of DRL in the head, chest and abdomen-pelvis areas as measured by CTDI vol were 14.9-24.1, 1.8-4.5, and 2.0-7.5 mGy, respectively, by age grouping; the typical values of DRL as measured by SSDE WD were 14.7-18.9, 4.2-6.9, and 4.7-11.8 mGy, respectively; the typical values of DRL as measured by DLP were 260-505, 40-185 and 64-435 mGy·cm. The typical values of DRL measured by CTDI vol were 1.8-6.8 and 2.2-9.2 mGy for the chest and abdomen-pelvis region, respectively, by d grouping; the typical values of DRL measured by SSDE WD were 4.2-9.1 and 4.9-13.0 mGy; typical values of DRL as measured by DLP were 40-255 mGy·cm and 85-545 mGy·cm, respectively. The typical values of DRL measured by CTDI vol were 14.1-23.1 mGy for head grouping by LAT; the typical values of DRL measured by SSDE WD were 14.3-18.5 mGy. The typical values of DRL measured by DLP were 240-475 mGy·cm. The CTDI vol was larger than SSDE WD in the head except for the (<1 year and <12.5 cm) subgroup, and the CTDI vol in head was (18.63±3.24) mGy and SSDE WD was (16.38±1.81) mGy, the difference was statistically significant ( t= 48.78, P < 0.001). The CTDI vol was smaller than SSDE WD within each subgroup in chest and abdomen-pelvis, the CTDI vol of chest was (2.77±1.02) mGy, and SSDE WD was (5.22±1.26) mGy with a statistically significant difference ( t=-210.89, P < 0.001); the CTDI vol of abdomen-pelvis was ( 3.36 ± 1.82) mGy and SSDE WD was (6.27 ± 2.44) mGy. The difference was also statistically significant ( t = -115.16, P < 0.001). Conclusions:The typical values of DRLs in the hospital are at a reasonable and low level compared with those in other countries, and SSDE WD reflects radiation dose more accurately than CTDI vol.Therefore there is an urgent need to establish DRLs based on SSDE WD.