British Journal of Radiology (2004) 77, 370-371
© 2004 British Institute of Radiology
doi: 10.1259/bjr/14928972
Whole-body CT health screening
A K Dixon, MD, FRCR, FRCP
Department of Radiology, Addenbrooke's NHS Trust and the University of Cambridge, UK
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Introduction
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Screening is an emotive issue. But with around one in three people being diagnosed with cancer at some stage during their lifetime and approximately one in four dying from cancer, it is not surprising that the public has become alarmed. Screening the healthy population for cancer seems such an obvious solution and most Western countries now offer some form of screening for breast cancer. Colon cancer is another prevalent killer: if polyps can be detected at an early stage and cancer prevented that must be a good thing — or is it? Likewise if CT can show coronary artery disease at an early stage, people might be persuaded to change their lifestyles to an extent which might save lives. So what is the problem? Surely with increasingly sophisticated technology, it should be simple to roll out CT screening for many forms of cancer and other serious disease. However, the evidence that people live longer and more happily because of screening is scant at best. For example, coronary artery calcification is part of the natural ageing process and few people radically alter their lifestyles to the extent of improving health.
Furthermore, screening tests are not without risk and must be done well if they are to succeed. For example, there is now no place for the amateur radiologist "doing a few mammograms" a year. Those involved in breast screening must be part of a multidisciplinary team and their results must be subjected to regular audit. I would imagine that the same form of audit should apply to those doing whole-body CT screening. Only by such scrutiny do the false positive and negative results become acceptable. Even to gain a reduction in mortality from breast cancer (but not necessarily overall mortality), it is likely that most women subjected to regular screening between the ages of 50 years to 70 years will endure the anxiety caused by at least one false positive mammogram result at some stage during their 20 years of screening. The lessons learnt by those who have so successfully pioneered the introduction of breast screening should be heeded by those introducing whole-body CT screening [1].
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Generic cancer screening
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There are considerable ethical issues associated with unselected "whole-body screening". It is pertinent to ask why individuals (we cannot yet call them patients) attend a CT screening centre in the first place. Given the current uncertainty about effectiveness of such activities, it is most unlikely that they have been referred by a General Practitioner (the Referrer under the Ionising Radiation (Medical Exposures) Regulations (IR(ME)R) 2000; www.doh.gov.uk/irmer.htm). A few may self-refer having had the scheme recommended by friends who have been "reassured" by a normal CT examination. More likely they have been influenced by information in life-style journals or by direct advertising by the centres. In such cases, the radiologist at the centre becomes the Referrer – and must assume appropriate responsibility for that role. Inevitably there may be a conflict of interest when the same person effectively acts as referrer, operator and practitioner. If the radiologist does assume that responsibility, there must be frank discussion and information leaflets pointing out that screening may identify numerous confusing benign conditions for which subsequent investigation may pose some risk (e.g. biopsy of benign hepatic lesion). Future health and life insurance may become more expensive.
Then comes the issue of who is responsible, medically and financially, for organizing further investigations. In the very few cases found to have a likely cancer, this might be viewed as a reasonable charge on the National Health Service in the UK and on insurance schemes elsewhere. However many incidental findings will arise for which the individual (perhaps now a patient) will seek advice. Is the radiologist the best person to provide such advice? Why should the GP do this at no charge? Why should any society pick up the cost of such further investigations? For example a probable benign renal cyst may be found (as in around 60% of the normal population aged 60 years); most whole body CT screening is done without intravenous contrast medium; several cysts will then be deemed indeterminate and require further imaging. Who should pay? Probably the individual. Whatever the findings at CT screening, it is essential that the individual/patient is not abandoned thereafter. Indeed one potential cause for litigation might be that counselling and subsequent follow up, whether necessary or unnecessary, is suboptimal.
Hillman elegantly detailed the potential outcomes of CT screening in a recent review in Radiology [2]. The true positive — a rare enough event — will result in a cancer being detected at an earlier stage than would otherwise have been the case: the patient is impressed and the benefits of screening CT will be extolled. But there is, as yet, little evidence that the patient will necessarily live longer because of the CT discovery (on account of the lead time bias, etc. [3]). The true negative will reassure the patient who may feel justified in continuing with existing life-style habits. The false positive result will lead to a worrying and, maybe, expensive sequence of tests and continuing anxiety [4]. The false negative will result in anguish all round: the individual will feel cheated that the disease was not picked up early enough despite screening; the radiologist will feel guilty that the lesion was not detected and may suffer further embarrassment in the courts. This is far from a win–win situation.
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Targeted cancer screening
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Targeted CT screening is a somewhat more straightforward concept. The individual with an extensive smoking history is clearly at increased risk of bronchial carcinoma. And a large study at the Mayo Clinic detected 40 cancers in a cohort of 1520 such individuals recruited for thoracic CT screening [5]. However a nodule requiring follow up was found in nearly 70% of all individuals, who then required quite extensive counselling. A real cynic could argue that even the 40 patients in whom a tumour was found merely had their lead time prolonged. Hence the importance of the ongoing randomized American College of Radiology Imaging Network (ACRIN) trial which will eventually produce the answer we want: namely, does CT screening in individuals with a heavy smoking history lead to a reduced cancer specific mortality? At present only very enthusiastic workers in the field would say that CT screening for lung cancer is cost-effective [6, 7].
CT colonography is probably as good as any other method of screening the colon for polyps 6 mm and over in diameter [8]; the benefits over conventional endoscopic colonoscopy in terms of morbidity and visualizing the entire colon are comparable with the potential advantage of immediate endoscopic biopsy. It will be interesting to see the results of the Health Technology Assessment trial of CT colonography in the current colon cancer screening trials (http://www.ncchta.org/ProjectData/l_project_record_not_published.asp?PjtId=1366).
Unfortunately the results will not be available for some time. Never the less, even today, if someone has a very strong family history of colon cancer and is advised to have regular check ups, a case for using a CT technique could easily be made. However, as far as untargeted screening is concerned, it must be remembered that early colon cancer will not be detected in the unprepared colon using the procedures offered by the majority of screening centres.
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Screening for disease other than cancer
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Coronary artery calcification screening is also rather speculative despite having been around for several years; only recently have the results from spiral CT reached those attained by electron beam CT. In male individuals, deposition of calcium along the coronaries is part of the normal ageing process. CT may provide evidence that the "calcium score" is greater than it should be for age and gender. However there is little evidence that drug treatment or life-style changes will have much effect. In a woman, the absence of calcification can be taken as some sign of good health, but not necessarily in a man. Indeed some CT screening centres in the USA are becoming concerned about potential litigation issues pertaining to a report stating "no coronary calcification seen" followed by a myocardial-related death in the weeks after screening. The implication is that "no calcification" does not necessarily mean normal; therefore the test is seen to be flawed. Never the less some claim that coronary artery calcium screening is cost-effective [9].
Other aspects that might be included in a whole-body CT screen could be bone mineral evaluation and body composition [10]. But it is difficult to reverse the development of osteoporosis and knowledge that there is too much intra-abdominal fat will not often lead to a therapeutic improvement.
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Conclusion
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Over-riding all these aspects is the thorny issue that while screening may lower mortality from an individual cancer, it may not necessarily lower overall mortality. Some patients will die from unrelated causes rather than from the cancer that was "cured" following detection by screening [3]. Another topical issue is the question of walk-in screening centres offering to "save lives" by whole-body CT screening, sometimes for profit. In the UK, the National Screening Committee has suggested that the National Health Service should not offer such screening at present (Muir Gray, personal communication). Many sources suggest that a radiologist's private practice should mirror their NHS practice. The current radiological and radiographic workforce can barely cope with the existing workload, let alone such new ventures. It will be interesting to hear what other countries recommend. Several observers have noted that such walk-in centres are usually located in relation to educated health-conscious consumers who can afford such procedures [11]!
So, here is yet another review article illustrating the current controversy [12, 13]. Hard facts from primary research are urgently needed. But I cannot see too many grant giving bodies rushing to assess what is currently viewed as a somewhat opportunistic and entrepreneurial endeavour.
Received for publication January 16, 2004.
Accepted for publication February 3, 2004.
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References
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- Kopans DB, Monsees B, Fieg SA. Screening for cancer: when is it valid? Lessons from the mammography experience. Radiology 2003;229:319–27.[Abstract/Free Full Text]
- Hillman BJ. CT screening: who benefits and who pays. Radiology 2003;228:26–8.[Free Full Text]
- Black WC, Ling A. Is earlier diagnosis really better? The misleading effects of lead time and length biases. AJR Am J Roentgenol 1990;155:625–30.[Free Full Text]
- Black WC. Overdiagnosis: an underrecognized cause of confusion and harm in cancer screening (editorial). J Natl Cancer Inst 2000;92:1280–2.[Free Full Text]
- Swensen SJ, Jett TR, Hartman TE, et al. Lung cancer screening with CT: the Mayo Clinic experience. Radiology 2003;226:756–61.[Abstract/Free Full Text]
- Miettinen OS. Screening for lung cancer: can it be cost-effective? Can Med Assoc J 2000;162:1431–6.[Medline]
- Wisnivesky JP, Mushlin AL, Sicherman N, Henschke C. The cost-effectiveness of low-dose CT screening for lung cancer: preliminary results of baseline screening. Chest 2003;124:614–2.[Abstract/Free Full Text]
- Fenlon HM, Nunes DP, Schroy PC, Barish MA, Clarke PD, Ferrucci JT. A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 1999;341:1496–503.[Abstract/Free Full Text]
- Shaw LJ, Raggi P, Berman DS, Callister TQ. Cost effectiveness of screening for cardiovascular disease with measures of coronary calcium. Prog Cardiovasc Dis 2003;46:171–84.[CrossRef][Medline]
- Ashwell M, Cole TJ, Dixon AK. New insight into the anthropometric classification of fat distribution revealed by computed tomography. Br Med J 1985;290:1692–4.
- Illes J, Fan E, Koenig BA, Raffin TA, Kann D, Atlas SW. Self-referred whole-body CT imaging: current implications for health care consumers. Radiology 2003;228:346–51.[Abstract/Free Full Text]
- Broadbent M. Freestanding, self referral centres for whole-body CT screening should be closed, or at least restricted to at-risk patients. Against the proposition. Med Phys 2003;30:2570–1.[Medline]
- Morin R. Free-standing, self referral centers for whole-body CT screening should be closed, or at least restricted to at-risk patients. For the proposition. Med Phys 2003;30:2569–70.[CrossRef][Medline]
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Introduction
Generic cancer screening
