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Patient-level dose monitoring in computed tomography: tracking cumulative dose from multiple multi-sequence exams with tube current modulation in children

Abstract

Background

In children exposed to multiple computed tomography (CT) exams, performed with varying z-axis coverage and often with tube current modulation, it is inaccurate to add volume CT dose index (CTDIvol) and size-specific dose estimate (SSDE) to obtain cumulative dose values.

Objective

To introduce the patient-size-specific z-axis dose profile and its dose line integral (DLI) as new dose metrics, and to use them to compare cumulative dose calculations against conventional measures.

Materials and methods

In all children with 2 or more abdominal-pelvic CT scans performed from 2013 through 2019, we retrospectively recorded all series kV, z-axis tube current profile, CTDIvol, dose-length product (DLP) and calculated SSDE. We constructed dose profiles as a function of z-axis location for each series. One author identified the z-axis location of the superior mesenteric artery origin on each series obtained to align the dose profiles for construction of each patient’s cumulative profile. We performed pair-wise comparisons between the peak dose of the cumulative patient dose profile and ΣSSDE, and between ΣDLI and ΣDLP.

Results

We recorded dose data in 143 series obtained in 48 children, ages 0–2 years (n=15) and 8–16 years (n=33): ΣSSDE 12.7±6.7 and peak dose 15.1±8.1 mGy, ΣDLP 278±194 and ΣDLI 550±292 mGy·cm. Peak dose exceeded ΣSSDE by 20.6% (interquartile range [IQR]: 9.9–26.4%, P<0.001), and ΣDLI exceeded ΣDLP by 114% (IQR: 86.5–147.0%, P<0.001).

Conclusion

Our methodology represents a novel approach for evaluating radiation exposure in recurring pediatric abdominal CT examinations, both at the individual and population levels. Under a wide range of patient variables and acquisition conditions, graphic depiction of the cumulative z-axis dose profile across and beyond scan ranges, including the peak dose of the profile, provides a better tool for cumulative dose documentation than simple summations of SSDE. ΣDLI is advantageous in characterizing overall energy absorption over ΣDLP, which significantly underestimated this in all children.

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Correspondence to Sjirk J. Westra.

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Supplementary Information

Online Supplementary Material 4
figure5

Graph displays the profiles of WED (water-equivalent diameter), mA and radiation dose in a 75-year-old woman (height: 163 cm, weight: 48 kg) who underwent contiguous chest and abdominopelvic examinations at 120 kV (beam width: 19.2 mm, helical pitch: 1) (PNG 1037 kb)

Online Supplementary Material 1

Direct calculation versus Monte Carlo simulation of z-axis dose profile (DOCX 16 kb)

Online Supplementary Material 2

Demographics of 15 children under 2 years of age who underwent multiple abdominal CT acquisitions and summated dose descriptors (DOCX 16 kb)

Online Supplementary Material 3

Demographics of 33 children ages 8–16 years who underwent multiple abdominal CT acquisitions and summated dose descriptors (DOCX 19 kb)

High resolution image (TIFF 154 kb)

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Tabari, A., Li, X., Yang, K. et al. Patient-level dose monitoring in computed tomography: tracking cumulative dose from multiple multi-sequence exams with tube current modulation in children. Pediatr Radiol (2021). https://doi.org/10.1007/s00247-021-05160-2

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Keywords

  • Abdomen
  • Children
  • Computed tomography
  • Cumulative radiation dose
  • Quality improvement
  • Radiation safety