Purpose or Case Report: Scanner console-provided volume CT Dose Index (CTDIvol) and Dose Length Product (DLP) are frequently added up inappropriately to obtain cumulative dose values in patients exposed to multiple multi-sequence CT exams, performed with varying z-axis coverage and often with longitudinal tube current modulation. We present the patient-size specific Dose Line Integral (DLI) as a new metric that allows this task to be performed in a more precise fashion across multiple scanner platforms
Methods & Materials: We reviewed all pediatric abdominal CT scans performed from 2013 through 2019 in patients who had at least two scans performed during the study period, recorded CTDIvol and DLP, and calculated Size Specific Dose Estimates (SSDE) for all scans with commercially available software. One author mapped an anatomic landmark (the take-off of the superior mesenteric artery from the aorta) to the z-axis position of each (sub)acquisition, to align the scans for construction of DLI curves as a function of z-axis location. The areas under these curves were then integrated and their sum calculated for all acquisitions each patient underwent. For each patient, z-axis-dependent cumulative DLI dose profiles were compared with summated SSDEs, and summated areas under all DLI curves were compared with summated DLPs
Results: We recorded data in 143 scans obtained in 48 patients, ranging in ages from 0-1 (n=15), 8-10 (n=21), 11-14 (n=7) and 15 (n=5) years. Number of scans per patient ranged from 2 to 6. The accumulated maximum point dose value of DLI was different from SSDE by an average of 24±14% (18.1 vs 15.5 mGy), ranging from -32% (6.8 vs 10.0 mGy) to +81% (46.3 vs 25.6 mGy). Globally-absorbed DLI exceeded summated DLPs by an average of 118±39% (649 vs 319 mGycm), ranging from 35% (1002 vs 742 mGycm) to 194% (273 vs 93 mGycm)
Conclusions: The graphic dose profile DLI gives a complete description of z-axis dose distribution for the studied CT examinations under a wide range of patient variables and acquisition conditions. Visualization of DLI profiles across and beyond the scan ranges provided a more precise tool for cumulative dose documentation than simple arithmetic summations of CTDIvol, SSDE and DLP. Accumulated dose estimates from simple summation of these conventional dose values substantially underestimated those calculated with the more precise DLI method in the majority of patients. This improved characterization of cumulative absorbed dose will guide better dose optimization efforts in this vulnerable population