IMAGING & ONCOLOGY - Society of Radiographers

18that a 40-year-old undergoing CT coronary angiography would have an estimated onein 270 chance of developing cancer (one in 600 in males). This article suggested thatfor 20-year-old patients the risk approximately doubles.Radiologists involved in CTC have been aware of the high levels of radiationassociated with the thin sections necessary for diagnostic studies and have alreadymade signifi cant improvements in reducing the dose 29 . Routine barium enema hasa radiation burden of about 10 mSv compared with standard CTC doses of 23 mSV.However, the dose of the CTC can be reduced to 5.7 mSv using low dose techniques 30 .Putting this in context for the general public, the average UK annual dose from naturalradiation is 2 mSv, 8 mSv if you live in Cornwall. With the further development ofimproved dose modulation techniques and fl at plate technology, the CTC radiation dosewill reduce even further.Although there have been signifi cant developments in MR colonography, they havenot reached the advanced stage of CTC, but the absence of ionising radiation makesthis a very attractive proposition for the future.One of the challenges within the screening population arises from the CTC’s sensitivity,ie what to confi dently report. The overcalling of small lesions, where CTC’s specifi cityis lower, will potentially subject otherwise well patients to the risk of unnecessarycolonoscopy and increase the overall cost of the screening programme. For this reason,the consensus is that only polyps of 6mm and above should be reported 31 .A second challenge, within the screening population, is dealing with the extra colonicfi ndings, many of which will be of no signifi cance 32,33 . Up to 6 per cent of patients (9per cent in the elderly age group) will need potentially expensive further investigation.Clearly a signifi cant number of these fi ndings will, however, be important. In a seriesof over 10,000 asymptomatic screened patients, one in 300 had an unsuspected extracolonic cancer and fi nding these tumours early was shown to be of fi nancial benefi t 34 .Financially CTC for screening remains a viable option.It seems almost certain that CTC will continue to go from strength to strength,replacing the barium enema and increasingly challenging colonoscopy as theinvestigation of choice for symptomatic colonic pathology and the screeningpopulation. The test now for the radiology community is how to cope with thispotential explosion of examinations with the limited resources of CT scanner access,appropriately trained radiographers and radiologists.Who knows, perhaps the lead of President Obama will effect further change withinthe UK?Bruce Fox is a consultant GI radiologist based in Derriford Hospital,Plymouth. He is peninsula head for the Postgraduate School of Radiology,and is radiology adviser for the development of NICE colonic surveillanceguidelines.Figure 4: A small colonic polyp highlighted in blue by the CAD system Figure 5: A CTC image for an incomplete optical colonscopy because of a stenotic recto-sigmoid tumour (image a)and a second tumour found in the caecum (image b shown with arrows. The rectosigmoid tumour is marked with an asterisk).2010IMAGING &ONCOLOGY