'Virtual colonoscopy' using CT scans is more effective for investigating patients with possible bowel cancer than an X-ray test, says a new study.
The researchers say that this less invasive CT colonography (CTC) should now be considered alongside the ‘gold standard’ of colonoscopy. However, they caution that guidelines are needed before this type of scan is used more widely because its ability to detect relatively unimportant issues can result in patients being referred for unnecessary follow-up tests.
The research was conducted by scientists at Imperial College London and University College London (UCL) with funding from the National Institute for Health Research Health Technology Assessment Programme, Cancer Research UK and the Engineering and Physical Sciences Research Council.
We have shown that CTC offers a viable option for people who are not able to or do not wish to undergo a colonoscopy for whatever reason.
– Professor Wendy Atkin
Department of Surgery and Cancer
In the first of the two trials published in The Lancet today, more than 3,800 patients were given either a CTC or the traditional test, a barium enema. The researchers showed that CTC was more effective than barium enema at finding bowel cancers and precancerous polyps.
Professor Steve Halligan of UCL, the joint-lead researcher, said: “Our trial shows that CTC is more accurate than barium enema. We hope that barium enema will now be phased out in favour of CTC and that NICE will update its guidelines. Although CTC can be performed on standard CT scanners available in practically all NHS hospitals, many do not have radiologists experienced with looking at CTC scans. These radiologists will need training in order to deliver the results we observed in our trials.”
In a second trial, almost 1,600 patients were given either a CTC or a colonoscopy. Previous studies have shown that these two tests have similar sensitivity for detecting bowel cancer.
Unlike colonoscopy, samples of tissue cannot be taken using CTC and it was not known how many patients needed a follow-up test to either confirm a suspected cancer or to rule out other findings found in the scan. Similarly, it was not known how many patients needed a follow-up test after colonoscopy because the scope could not pass around the bowel.
In patients who had CTC, 30 per cent had a follow-up test compared with only eight per cent who had colonoscopy. Some of the follow-up tests after CTC were necessary because a possible cancer or large polyp had been seen. However, almost a third of follow-up tests were to investigate small polyps that could have been left alone because they are unlikely to develop into cancers.
Professor Wendy Atkin of the Department of Surgery & Cancer at Imperial College London, also a joint-lead researcher, said: “Understandably hospital doctors are cautious in requesting more tests after CTC. However, CTC detects unimportant findings, so guidelines are needed to help doctors decide who should have a further test. With these in place, we have shown that CTC offers a viable option for people who are not able to or do not wish to undergo a colonoscopy for whatever reason.”
CTC works by taking hundreds of x-ray 'slices' through the body which are then processed by a computer to create a ‘virtual’ 3D image of the inside of the bowel, similar to what is seen during colonoscopy. CTC is a less uncomfortable test and, unlike colonoscopy, patients do not need to be sedated.
Professor Jane Wardle from UCL, who led studies looking into patient experiences of the three tests, said: “We have shown that people prefer CTC to both barium enema and colonoscopy. This research should mean that patients with bowel cancer symptoms can get the best test for them.”
Sara Hiom, Cancer Research UK’s director of early diagnosis, said: "Survival rates for bowel cancer have doubled over the last 40 years thanks to better treatments and improved ways of diagnosing the disease. This research will mean that anyone with a suspected bowel cancer has two effective options to further investigate their symptoms."
Based on a news release by Cancer Research UK
Halligan, S. et al. 'Computed tomographic colonography versus double contrast barium enema for diagnosis of colorectal cancer or large polyps in symptomatic patients: a multicentre randomised trial in clinical practice.' The Lancet, Early Online Publication, 14 February 2013 doi:10.1016/S0140-6736(12)62124-2
Atkin, W.S. et al. 'Computed tomographic colonography versus colonoscopy for investigation of patients with symptoms of colorectal cancer: a multicentre randomised trial in clinical practice.' The Lancet, Early Online Publication, 14 February 2013 doi:10.1016/S0140-6736(12)62186-2
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