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Call for radiation doses from CT scans to be more consistent

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Large differences in radiation doses used for computed tomography (CT) scans are mainly due to how the scanners are used by staff rather than differences in patients or machines, a study suggests.

Setting more consistent dose standards should, therefore, be possible and will ensure that patients are not exposed to unnecessary radiation risks, researchers said in the British Medical Journal.

“These findings suggest that optimising doses to a consistent standard is possible, which will probably require more education”

Study authors

They noted that CT radiation was associated with an increased risk of cancer, so it was important to minimise exposure and reduce unnecessary variation during scanning.

They cited evidence that doses were highly variable across patients and institutions and, in many cases, could be reduced by 50% or more without reducing image quality and diagnostic accuracy.

To better understand the factors contributing to this variation, the international research team analysed dose data for over two million CT scans from 151 institutions, across seven countries.

They included scans of the abdomen, chest, combined chest and abdomen, and head from 1.7 million adults between November 2015 and August 2017.

They adjusted the data for a range of variables related to the patient, institution and machine – for example, manufacturer and model.

The researchers found that most of these factors had only a small effect on dose variation across countries.

For example, after adjusting for patient characteristics, there was still a fourfold range in mean effective dose for abdominal scans and a 17-fold range in proportion of high dose scans, from 4-69%.

Similar variation persisted for chest scans, and combined chest and abdomen scans, said the researchers. Adjusting for institution and machine factors also had little effect on dose variation.

However, adjusting for technical factors – how scanners were used by clinical staff – substantially reduced or eliminated nearly all the dose variation across countries, they said.

The researchers concluded the dose variation used for CT scanning was primarily driven by how scanners were used, rather than to underlying differences in patients scanned or the machines used.

Although an observational study, the researchers said their findings suggested that optimising doses to a consistent standard should be possible.

They called for more education and international collaboration to set benchmarks for optimum target doses.

“These findings suggest that optimising doses to a consistent standard is possible, which will probably require more education of individuals who create protocols for CT, recalibration of image quality expectations targeted to answering the clinical question at hand, and greater sharing of protocols across institutions,” they stated.

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