Understanding, justifying, and optimizing radiation exposure for CT imaging in nephrourology


An estimated 4–5 million CT scans are performed in the USA every year to investigate nephrourological diseases such as urinary stones and renal masses. Despite the clinical benefits of CT imaging, concerns remain regarding the potential risks associated with exposure to ionizing radiation. To assess the potential risk of harmful biological effects from exposure to ionizing radiation, understanding the mechanisms by which radiation damage and repair occur is essential. Although radiation level and cancer risk follow a linear association at high doses, no strong relationship is apparent below 100 mSv, the doses used in diagnostic imaging. Furthermore, the small theoretical increase in risk of cancer incidence must be considered in the context of the clinical benefit derived from a medically indicated CT and the likelihood of cancer occurrence in the general population. Elimination of unnecessary imaging is the most important method to reduce imaging-related radiation; however, technical aspects of medically justified imaging should also be optimized, such that the required diagnostic information is retained while minimizing the dose of radiation. Despite intensive study, evidence to prove an increased cancer risk associated with radiation doses below ~100 mSv is lacking; however, concerns about ionizing radiation in medical imaging remain and can affect patient care. Overall, the principles of justification and optimization must remain the basis of clinical decision-making regarding the use of ionizing radiation in medicine.

Key points

  • CT scans are commonly performed in nephrourology, for indications including suspected stones and renal masses.

  • Concerns have been raised regarding the potential harmful effects of exposure to radiation associated with CT scans; however, the dose associated with CT is <~100 mSv and no harmful effects have been shown at these low doses.

  • Even taking the very low potential risk of malignancy into account, such a risk must be considered in the context of the clinical benefit of performing the scan, and elimination of unnecessary CT examinations is the first step towards managing risk.

  • Optimization of the scanning technique is essential, so that the necessary clinical information can be gathered with minimization of the radiation dose.

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Fig. 1: Illustration of the different models for radiation-related cancer risk as a function of radiation dose in the low-dose (<100 mSv) region.
Fig. 2: Cancer incidence as a function of effective radiation dose for survivors of the atomic bombings in Japan.
Fig. 3: Typical dose levels (in terms of effective dose) for a routine CT examination of the abdomen and pelvis over various time periods.
Fig. 4: Typical effective doses for common imaging examinations that use ionizing radiation.


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The project described was supported by grant number DK 100227 from the National Institutes of Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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C.H.M., A.F. and N.T. researched data for the article. C.H.M., A.F., T.J.V., A.K. and J.C.L. made substantial contributions to discussions of content. C.H.M. and A.F. wrote the manuscript. All authors reviewed and edited the manuscript before submission.

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Correspondence to Cynthia H. McCollough.

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C.H.M. is the principal investigator of a grant to the authors’ institution from Siemens Healthcare that is unrelated to this work. The other authors declare no competing interests.

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Ferrero, A., Takahashi, N., Vrtiska, T.J. et al. Understanding, justifying, and optimizing radiation exposure for CT imaging in nephrourology. Nat Rev Urol 16, 231–244 (2019). https://doi.org/10.1038/s41585-019-0148-8

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