A single pediatric CT scan increases the risk of brain cancer

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Children and young adults who are exposed to a single CT scan of the head or neck before the age of 22 have a significantly increased risk of developing a brain tumor, particularly glioma, after at least five years, according to the results of the great EPI-CT study.

“Translation of our risk estimates to the clinical setting indicates that for every 10,000 children who received a CT examination of the head, approximately one radiation-induced brain cancer is expected during the 5 to 15 years following the CT examination,” noted lead author Michael Hauptmann, PhD. , Institute for Biostatistics and Record Research, Brandenburg Medical School, Neuruppin, Germany, and coauthors.

“In addition to the clinical benefit of most CT scans, there is a small risk of cancer from radiation exposure,” Hauptmann said. Medscape Medical News.

“So CT scans should only be used when necessary, and if used, the lowest possible dose should be applied,” he said.

The study was published online December 6 in The Lancet Oncology.

“This is a thoughtful and well-conducted study by a leading multinational team of scientists that adds further weight to the growing body of evidence that has found that exposure to CT scans increases a child’s risk of developing brain cancer,” said Rebecca Bindman. -Smith, MD, of the University of California, San Francisco (UCSF), who was not involved in the research.

“The results are real and important,” he said. Medscape Medical News, adding that “the authors were conservative in their assumptions and performed a large amount of sensitivity analysis… to verify that the results were robust to a wide range of assumptions, and the results changed relatively little.”

I don’t think there is enough awareness [about this risk]”Hauptmann said. “There is evidence that a non-negligible number of TCs are not warranted according to the guidelines, and there is evidence that doses vary substantially for the same TC between institutions in the same or different countries.”

In fact, particularly in the United States, “we do a lot of CT scans on children and even more on adults that are just unnecessary,” agreed Bindman-Smith, a professor of epidemiology and biostatistics at UCSF. “It is important for patients and providers to understand that nothing we do in medicine is risk-free, including CT scanning. If a CT scan is necessary, the benefit almost certainly outweighs the risk. But if [not], then it must not be obtained. Both patients and providers must make carefully considered decisions before requesting or agreeing to CT.”

He also noted that while this study assessed the risk of brain cancer only, children who have head CT scans also have an increased risk of leukemia.

Dose-response relationship

The study included 658,752 people from nine European countries and 276 hospitals. Each patient had received at least one CT scan between 1977 and 2014 before their 22nd birthday. Eligibility requirements included being alive for at least 5 years after the first scan and not having been previously diagnosed with cancer or a benign brain tumor.

The absorbed radiation dose to the brain and 33 other organs and tissues was estimated for each participant using a dose reconstruction model that included historical information on CT machine settings, questionnaire data, and header metadata from Digital Imaging and communication in medicine (DICOM). “Mean brain dose per head or neck CT scan increased from 1984 to around 1991, following the introduction of multislice CT scanners, at which time the mean dose decreased and then leveled off around 2010,” the researchers write. authors.

During a median follow-up of 5.6 years (beginning 5 years after the first scan), 165 brain cancers occurred, including 121 (73%) gliomas, as well as a variety of other morphologic changes.

The mean cumulative brain dose, delayed 5 years, was 47.4 mGy overall and 76.0 mGy among people with brain cancer.

“We observed a significant positive association between the cumulative number of head or neck CT examinations and the risk of all brain cancers combined (P < .0001), and gliomas separately (P = 0.0002),” the team reports, adding that for a brain dose of 38 mGy, which was the average head or neck CT dose in 2012-2014, the relative risk of developing brain cancer was 1. 5, compared with not having a CT scan, and the absolute excess risk per 100,000 person-years was 1.1.

These findings “can be used to provide patients and their parents with important information about the risks of CT examination to balance them against the known benefits,” said Nobuyuki Hamada, PhD, of the Central Research Institute of Electric Power Industry, Tokyo, Japan, and Lydia. B Zablotska, MD, PhD, of UCSF, writing in a linked comment .

“In recent years, CT use rates have been steady or declining, and various efforts have been made (eg, in terms of diagnostic reference levels) to justify and optimize CT examinations. Such Continued efforts, along with extended epidemiologic investigations, would be necessary to minimize the risk of brain cancer after pediatric CT examination,” they add.

Keep the dose to a minimum

The study’s finding of a dose-response relationship underscores the importance of keeping doses to a minimum, Bindman-Smith said. “I don’t think we’re doing this enough,” she added.

“In the UCSF International CT Dose Registry, where we collected CT scans from 165 hospitals in many millions of patients, we found that the average brain dose for a head CT scan in a 1-year-old child is 42 mGy, but that this dose varies tremendously, where some children receive a dose of 100 mGy.

“So a second message is that CT scans should not only be justified and used judiciously, but they should also be optimized, that is, use the lowest possible dose. Personally, I think there needs to be regulatory oversight to ensure that patients receive the absolute lowest doses possible,” he added. “My team at UCSF has written quality measures endorsed by the National Quality Forum as a start to setting explicit standards for how CT should be performed to ensure that cancer risks are as low as possible.”

The study was funded through the Belgian Cancer Registry; La Ligue contre le Cancer, L’Institut National du Cancer, France; the Ministry of Health, Labor and Welfare of Japan; the Federal Ministry of Education and Research of Germany; World Cancer Research; the Dutch Cancer Society; the Research Council of Norway; Nuclear Safety Council, Generalitat de Catalunya, Spain; the US National Cancer Institute; the UK National Institute for Health Research; and Public Health England. Hauptmann has disclosed no relevant financial relationships of interest. The relevant financial relationships of other researchers are listed in the original article. The Hamada and Zablotska report did not reveal relevant financial relationships.

Lancet Oncol. Published online December 6, 2022. Summary, Commentary

Kate Johnson is a Montreal-based freelance medical journalist who has been writing for over 30 years on all areas of medicine.

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