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Patients undergoing recurrent CT scans: assessing the magnitude

An Editorial Comment to this article was published on 04 February 2020



To assess percent of patients undergoing multiple CT exams that leads to cumulative effective dose (CED) of ≥ 100 mSv and determine their age distribution.


Data was retrieved retrospectively from established radiation dose monitoring systems by setting the threshold value of 100 mSv at four institutions covering 324 hospitals. The number of patients with CED ≥ 100 mSv only from recurrent CT exams during a feasible time period between 1 and 5 years was identified. Age and gender distribution of these patients were assessed to identify the magnitude of patients in the relatively lower age group of ≤ 50 years.


Of the 2.5 million (2,504,585) patients who underwent 4.8 million (4,819,661) CT exams during the period of between 1 and 5 years, a total of 33,407 (1.33%) patients received a CED of ≥ 100 mSv with an overall median CED of 130.3 mSv and maximum of 1185 mSv. Although the vast majority (72–86%) of patients are > 50 years of age, nearly 20% (13.4 to 28%) are ≤ 50 years. The minimum time to accrue 100 mSv was a single day at all four institutions, an unreported finding to date.


We are in an unprecedented era, where patients undergoing multiple CT exams and receiving CED ≥ 100 mSv are not uncommon. While underscoring the need for imaging appropriateness, the consideration of the number and percent of patients with high exposures and related clinical necessities creates an urgent need for the industry to develop CT scanners and protocols with sub-mSv radiation dose, a goal that has been lingering.

Key Points

We are in an era where patients undergoing multiple CT exams during a short span of 1 to 5 years are not uncommon and a sizable fraction among them are below 50 years of age.

This leads to cumulative radiation dose to individual patients at which radiation effects are of real concern.

There is an urgent need for the industry to develop CT scanners with sub-mSv radiation dose, a goal that has been lingering.

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Biological Effects of Ionizing Radiation Board


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Cumulative effective dose




Effective dose


International Atomic Energy Agency


International Commission on Radiological Protection


National Council on Radiation Protection and Measurements


United Nations Scientific Committee on Effects of Atomic Radiation


World Health Organization


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The authors sincerely acknowledge the subject matter expertise provided by Prof. Fred Mettler (Emeritus Professor, University of New Mexico) and statistical assistance by Dr. Hui Zheng of MGH, and of Matthew Hough, at AdventHealth, for his aid in determining typical institutional radiation doses.


The authors declare that this work has not received any funding.

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Correspondence to Madan M. Rehani.

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The scientific guarantor of this publication is Madan Rehani.

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The authors declare that they have no conflict of interest.

Statistics and biometry

Dr. Hui Zheng, statistician, kindly provided statistical advice for this manuscript. He has been acknowledged.

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Written informed consent was waived by the Institutional Review Board.

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Institutional Review Board approval was obtained wherever IRB was available.

Institutional Review Board approval was not required at some as indicated in the manuscript.


• Retrospective

• Observational

• Multicenter study

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Rehani, M.M., Yang, K., Melick, E.R. et al. Patients undergoing recurrent CT scans: assessing the magnitude. Eur Radiol 30, 1828–1836 (2020).

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  • Radiation protection
  • Patient safety
  • Radiologic technology
  • Risk
  • Radiation dosage