CT Scans for Under-20s Raise Risk of Cancer | Stuff.co.nz

The risk of getting cancer increases for people who have CT scans before they are 20, a large Australian study has found.

The researchers who carried out the study, led by Professor John Matthews from the Melbourne University School of Population and Global Health, called for limits on the use of CT scans.

"Future CT scans should be limited to situations where there is a definite clinical indication, with every scan optimised to provide a diagnostic CT image at the lowest possible radiation dose," the study said.

While radiation doses from CT scans carried out now were likely to be lower than doses from scans done between 1985 and 2005, some increase in cancer risk was still likely, it said.

The study, published today on bmj.com, suggested young people who underwent CT scans were 24 per cent more likely to develop cancer compared with those who did not. But the researchers emphasised the number of extra cancers expected was low.

In a group of 10,000 young people, 39 cancers would be expected during the next 10 years, but if they all had one CT scan, there would be up to six extra cancers.

The 10.9 million people in the study cohort identified from Australian Medicare records were aged from 0-19 at the start of 1985, or were born from 1985 to 2005.

Of the group, 680,211 were exposed to CT scans at least 12 months before any cancer diagnosis. Of those who had scans, 18 per cent had more than one.

By the end of 2007, 3150 of the exposed group and 57,524 of the unexposed group had been diagnosed with cancer.

The incidence rate was 24 per cent greater in the exposed group after adjusting for age, gender and year of birth. Risk increased by 16 per cent for each additional CT scan.

Researchers acknowledged that in some cases, low-grade cancers in the brain may have given rise to symptoms that were investigated several years before they were finally diagnosed. Almost 60 per cent of CT scans were of the brain.

While they could not assume all excess cancers were caused by CT scans, they concluded the "increased incidence of many different types of cancer... is mostly due to irradiation".

Given that the study only included cancers diagnosed in cohort members up to the end of 2007, the "eventual lifetime risk from CT scans cannot yet be determined", the researchers said.

They recommend practitioners weigh the benefits against the potential risks to justify each CT scan decision.

In an accompanying editorial, Dr Aaron Sodickson from Harvard Medical School said it was important to recognise the incidence of cancer in children was extremely small, so "a 24 per cent increase makes this risk just slightly less small".

Many methods were available to manage radiation dose and with further validation of risk models, more accurate risk assessment could be performed to "better-inform imaging decisions".

For brain cancer, the incidence in the exposed group declined with time from the first CT-exposure, but brain cancer incidence was still significantly higher more than 15 years after the first exposure.

For other solid cancers (tumours as opposed to cancers of the blood or bone marrow) the absolute excess cancer incidence increased significantly with time since the first exposure.

For all cancers combined, the proportional increase declined with the number of years since the first CT scan, but was still higher at 15 or more years after the first exposure.

For brain cancer, the highest risk was for children exposed before the age of five. That risk decreased the older a child was at the first exposure. But for all cancers combined the risk remained significantly higher for those who were oldest (15-19 years) when they had their CT scan.

For solid cancers other than brain cancer, the proportional increase in risk was 23 per cent in females and 14 per cent in males.

- ? Fairfax NZ News

Source: http://www.stuff.co.nz/science/8704344/CT-scans-raise-youth-cancer-risk

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