We found that, compared with no screening, either 2-D or 3-D CT colonography is an effective and cost-effective test. Indeed, screening with 3-D CT colonography every 5 yr is more effective than any of our other modeled tests. Screening with 3-D CT colonography every 10 yr costs about $8,150 per life-year gained, and screening every 5 yr costs about $13,460 per life-year gained. Although there is no firmly established threshold for cost-effectiveness, these estimates are both comparable to those of generally accepted medical interventions (69
). One other recently published analysis reported similar findings for CT colonography every 10 yr; however, they did not examine the possibility of other intervals for testing, an important consideration given the non-invasive nature of CT colonography, and its status as a first screening step, analogous to sigmoidoscopy (71
While these findings support the argument that CT colonography be added to our armamentarium, the critical question is how CT colonography fares in comparison to current screening standards, particularly the gold standard of optical colonoscopy. Under base case assumptions, and indeed under most modeled conditions, 2-D CT colonography, and 3-D CT colonography every 10 yr, are not cost-effective relative to optical colonoscopy every 10 yr. There were only two exceptions to this rule. The first is if the costs of CT colonography are substantially (at least three to four times) lower than those of optical colonoscopy. The second is if nearly all of those with adenomas found on CT have a follow-up optical colonoscopy and polypectomy. However, in randomized trials of screening, follow-up happens in about 75% of cases (58
). Exceeding this would require dedicated resources; an intriguing option, now done at some centers, is same-day optical colonoscopy after CT colonography. Indeed, given the difficulty in bowel preparation for these procedures, such “all-in-one” type screening visits may be the preferable option to optimize adherence and the only way to ensure the cost-effectiveness of CT colonography.
We found that 3-D CT colonography done every 5 yr is the most effective of our primary modeled tests. However, in the base case, it costs $156,000 per life-year gained compared with optical colonoscopy every 10 yr, a figure that is considered expensive relative to most medical interventions (69
). Our sensitivity analyses suggest that there is substantial uncertainty around this incremental cost-effectiveness ratio. CT colonography every 5 yr is a dominant strategy if CT colonography costs less than $400 or if optical colonoscopy costs more than $1,000. Similarly, CT colonography every 5 yr is a dominant strategy if the ratio of the cost of optical colonoscopy to CT colonography is greater than 1.6; a ratio of 1.5 leads to an incremental cost-effectiveness ratio for CT colonography of less than $50,000 per life-year gained, and a ratio of 1.3 to an incremental cost-effectiveness ratio of less than $100,000 per life-year gained. Our figures can help to guide a reasonable reimbursement for CT colonography.
Perhaps most important from a clinical perspective is that the incremental cost-effectiveness of 3-D CT colonography done every 5 yr is highly sensitive to test accuracy, particularly test sensitivity for 1 cm adenomas. If test sensitivity is lower than 83%, then CT colonography is almost never a preferred strategy versus
optical colonoscopy. There is little or no data on the diagnostic accuracy or reliability of primary 3-D interpretation of CT colonography in non-academic settings. Our analyses suggest that even with primary 3-D interpretation, CT colonography has a fairly small margin of error for adenoma sensitivity; thus, it is critical that issues of training and utilization of optimal technology be considered before CT colonography is disseminated (72
). Lower sensitivity levels, such as those found in trials with primary 2-D interpretation, essentially rule out CT colonography as a cost-effective option compared with optical colonoscopy (13
Another important issue is that of adherence. In our base analyses, we have only compared adherence under the assumption that it is comparable between tests. However, our analyses examining how differential adherence between FOBT and CT colonography impact cost-effectiveness are revealing; FOBT may be dominant if it is highly adhered to and CT colonography is not. We would note that for patients that would refuse screening other than CT colonography, nearly any application of CT colonography is cost-effective, as shown by the cost-effectiveness compared with no screening.
Our study has several limitations. There are no trials showing mortality reduction with CT colonography, and as with most models based on the natural history of a disease process, we relied on multiple data sources, which may bias results. We also have little data to guide us on reimbursement rates; indeed, we would view this analysis as a tool to help establish those rates. Further, there are several issues that are difficult to model accurately. One of these relates to extracolonic findings on CT colonography; the costs and benefits of these findings are completely uncertain. Another issue is the possibility of increased cancer risk related to radiation exposure. Recent analyses have suggested that these risks are very small for colonic imaging in a screening age population (75
). There are also resource implications to any shift in screening that may occur; we and others have shown that one limitation of colonoscopic screening is a lack of endoscopist supply (76
), and CT colonography may help to ameliorate this. This is the reason that we did not examine using more frequent (e.g., every 5 yr) colonoscopy in our scenarios; additionally, guidelines at present endorse 10 yr intervals for optical colonoscopy (7
). On the other hand, demands would be placed on radiologists and CT scanners, and it is uncertain whether increased demand for CT colonography can be met given current staffing models, although outsourcing of radiology interpretation may make this a more feasible alternative than increasing endoscopist supply.
Overall, our findings suggest that CT colonography is an effective test, particularly when done with primary 3-D interpretation at 5-yr intervals. Compared with no screening, it is cost-effective, and from this perspective we would argue that it belongs in our screening armamentarium. However, under our base case assumptions, screening with CT colonography is not likely to be cost-effective relative to screening with optical colonoscopy. There are conditions, particularly those related to the relative costs of optical and CT colonography, under which 3-D CT colonography done every 5 yr is a cost-effective or even a dominant strategy. On the other hand, the lower diagnostic test accuracy that is likely to be seen in general practice compared with academic settings, particularly early in the deployment of a new technique, may substantially decrease the effectiveness of CT colonography compared with optical colonoscopy (72
). CT colonography as a primary screening test should be implemented cautiously, with careful attention to ensuring accurate interpretation in non-academic settings, and a reimbursement rate that is significantly less than that of optical colonoscopy.
What Is Current Knowledge
- Computerized tomography (CT) colonography is a technology for colorectal cancer screening.
- The costs and benefits of computerized tomography colonography are uncertain.
What Is New Here
- CT colonography is expensive compared with colonoscopy.
- CT colonography can be cost-effective if low-priced and accurate.
- Three-dimensional imaging at 5-yr intervals is necessary for cost-effectiveness.