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CT dose survey in adults: what sample size for what precision?

  • Computed Tomography
  • Published:
European Radiology Aims and scope Submit manuscript

Abstract

Objectives

To determine variability of volume computed tomographic dose index (CTDIvol) and dose–length product (DLP) data, and propose a minimum sample size to achieve an expected precision.

Methods

CTDIvol and DLP values of 19,875 consecutive CT acquisitions of abdomen (7268), thorax (3805), lumbar spine (3161), cervical spine (1515) and head (4106) were collected in two centers. Their variabilities were investigated according to sample size (10 to 1000 acquisitions) and patient body weight categories (no weight selection, 67–73 kg and 60–80 kg). The 95 % confidence interval in percentage of their median (CI95/med) value was calculated for increasing sample sizes. We deduced the sample size that set a 95 % CI lower than 10 % of the median (CI95/med ≤ 10 %).

Results

Sample size ensuring CI95/med ≤ 10 %, ranged from 15 to 900 depending on the body region and the dose descriptor considered. In sample sizes recommended by regulatory authorities (i.e., from 10–20 patients), mean CTDIvol and DLP of one sample ranged from 0.50 to 2.00 times its actual value extracted from 2000 samples.

Conclusions

The sampling error in CTDIvol and DLP means is high in dose surveys based on small samples of patients. Sample size should be increased at least tenfold to decrease this variability.

Key Points

• Variability of dose descriptors is high regardless of the body region.

• Variability of dose descriptors depends on weight selection and the region scanned.

• Larger samples would reduce sampling errors of radiation dose data in surveys.

• Totally or partially disabling AEC reduces dose variability and increases patient dose.

• Median values of dose descriptors depend on the body weight selection.

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Acknowledgements

The scientific guarantor of this publication is Denis Tack. The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. One of the authors has significant statistical expertise. Institutional Review Board approval was obtained. Written informed consent was waived by the Institutional Review Board. This material has been presented at the ECR 2015. Methodology: retrospective, observational/experimental, multicenter study.

Author information

Authors and Affiliations

  1. Department of Radiology, Hôpital Ambroise Paré, Boulevard Président Kennedy 2, 7000, Mons, Belgium

    Stephen Taylor

  2. Department of Pneumology, Hôpital Erasme, Route de Lennik 808, 1070, Brussels, Belgium

    Alain Van Muylem

  3. Department of Radiology, Clinique des Grangettes, 7 Chemin des Grangettes, 1224, Chêne-Bougeries, Switzerland

    Nigel Howarth

  4. Department of Radiology, Hôpital Erasme, Route de Lennik 808, 1070, Brussels, Belgium

    Pierre Alain Gevenois

  5. Department of Radiology, EpiCURA, Clinique Louis Caty, rue Louis Caty 136, 7331, Baudour, Belgium

    Denis Tack

Authors
  1. Stephen Taylor
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  2. Alain Van Muylem
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  3. Nigel Howarth
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  4. Pierre Alain Gevenois
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  5. Denis Tack
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Corresponding author

Correspondence to Denis Tack.

Appendix 1

Appendix 1

Fig. 5

Fig. 5
figure 5

a-d: When using CTDIvol as the date source, these figures show the 95 % confidence interval in center A (open circles) and in center B (closed circles) in percentage of the median as a function of the sample size. Vertical lines correspond to the sample sizes ensuring CI95/med < 10 %. a: Head b: Cervical spine c: Lumbar spine d: Abdomen

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Fig. 6

Fig. 6
figure 6

a–d: When using DLP as the date source, these figures show the 95 % confidence interval in center A (open circles) and in center B in percentage of the median as a function of the sample size. Vertical lines correspond to the sample sizes ensuring CI95/med < 10 %. a: Head. b: Cervical spine. c: Lumbar spine. d. Abdomen

Full size image

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Taylor, S., Van Muylem, A., Howarth, N. et al. CT dose survey in adults: what sample size for what precision?. Eur Radiol 27, 365–373 (2017). https://doi.org/10.1007/s00330-016-4333-3

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  • DOI: https://doi.org/10.1007/s00330-016-4333-3

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