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Consensus on Current Clinical Practice of Virtual Colonoscopy

¹ Department of Radiology, 3D and Image Processing Center, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115.
² Department of Radiology, Boston Medical Center, 88 E Newton St., Boston, MA 02118.

Received April 18, 2004; accepted after revision July 22, 2004.

 
Address correspondence to M. A. Barish (mabarish{at}partners.org).

Abstract

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OBJECTIVE. The purpose of our study was to determine the current opinions regarding the performance, interpretation, reporting, and clinical role of virtual colonoscopy among a group of selected experts to develop a consensus statement.

MATERIALS AND METHODS. A questionnaire was sent to 33 selected experts in virtual colonoscopy. Responses were tabulated and results were used to develop a consensus statement. The results of the questionnaire and consensus statement were sent to respondents for comment and approval.

RESULTS. Thirty-one (93.9%) of 33 surveys were returned. Eighty-seven percent (27/31) of respondents believe virtual colonoscopy is a credible screening method. Oral sodium phosphate solution is the laxative preferred by more than 66% (18/27), whereas 62% (13/21) do not believe fecal tagging is necessary. All respondents (25/25) think that both prone and supine imaging is required, with most (81%, 21/26) believing IV contrast material is not necessary. The routine use of spasmolytics is suggested by only 15% (4/26). The largest acceptable slice thickness of 3 mm is agreed on by 88% (22/25). All respondents believe screening virtual colonoscopy should be performed at a lower dose per slice than conventional CT. Most (80%, 20/25) believe the optimum method of interpreting virtual colonoscopy should be primary axial review, with 3D used for problem solving. All but one respondent (96%, 26/27) agree there is a threshold size below which polyps are not clinically important. When reporting virtual colonoscopy results, 59% (16/27) believe polyps less than 4 mm need not be reported.

CONCLUSION. A consensus is developing among experts as to the appropriate manner in which virtual colonoscopy should be performed, interpreted, and reported.

Introduction

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Virtual colonoscopy or CT colonography is a rapidly evolving method for the detection of colorectal polyps and cancers. Multiple studies have shown that it has similar accuracy to conventional colonoscopy both in high-risk groups and, more recently, in a low-prevalence screening population [1–4]. Virtual colonoscopy is a viable alternative to existing screening tests for colorectal cancer because it is safe and noninvasive. However, issues relating to clinical implementation remain as virtual colonoscopy moves from being a research technique to becoming a generally accepted screening test.

Transitioning a new technology into clinical practice is facilitated by development of a set of standards and practice guidelines. Traditionally, development of such guidelines follows from an accumulation of clinical data, literature reviews, and consensus opinions from knowledgeable experts in the field. The goal of this study was to develop an expert consensus statement to help prepare guidelines for clinical practice. The methodology of using an initial questionnaire to survey opinions and allowing participating individuals to comment on the consensus statement and offer minority opinions allows a representative opinion of the current state of virtual colonoscopy.

Materials and Methods

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The authors developed a questionnaire (Appendix 1) to survey opinions of leading experts in virtual colonoscopy. Experts were selected from one of the following groups: radiologists with experience in performing and interpreting virtual colonoscopy, gastroenterologists familiar with virtual colonoscopy practices and having extensive experience in colorectal cancer screening programs, and other individuals familiar with virtual colonoscopy who represent health care policy decision makers. Selection of experts within these groups was based on the individual being a faculty member or invited speaker at the third or fourth International Symposium on Virtual Colonoscopy or being a lead author in a major virtual colonoscopy publication. Most selected experts were radiologists (26/31, 83.9%); however, two gastroenterologists, two primary care physicians, and the cofounder and chair of the Colon Cancer Alliance were also surveyed. A list of respondents and their primary specialties is in Appendix 2. Individuals were instructed to respond to questions on the basis of the current state of the technique of virtual colonoscopy at the time of the survey and to leave a question blank if they did not have knowledge or an opinion regarding the question. The results of the initial questionnaire were used to develop a consensus statement. Both the results of the questionnaire and the consensus statement were sent to the respondents for comment and approval. The returned approvals and comments were received and reviewed, and the comments were incorporated into the consensus statement. The modified consensus statement was then forwarded to respondents for final approval; additional comments were not solicited at this stage.

Results

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Questionnaire
Thirty-one (93.9%) of 33 surveys were returned with at least one response to a question. For the overall consensus statement, 87% (27/31) thought that virtual colonoscopy is currently a credible screening method but differed as to whether the test should be a third-line alternative after both conventional colonoscopy and barium enema (6/31, 19.4%), should replace the barium enema (16/31, 51.6%), or should be a first-line test equivalent to conventional colonoscopy (5/31, 16.1%). The most common response (16/31, 51.6%) was that "Virtual colonoscopy is currently a credible alternative screening method and should be considered the test of choice when a patient is unable or unwilling to undergo conventional colonoscopy." Only 16% (5/31) believe virtual colonoscopy should be offered to the general public as a replacement or alternative to conventional colonoscopy.

Technique.—Oral sodium phosphate solution (either single or double dose) is the preferred method used by more than 66% (18/27) of respondents. Most respondents (62%, 13/21) do not believe fecal tagging is necessary. Of those who do use fecal tagging (8/21), the preferred method was the use of compounds containing iodine (7/8), either alone (3/8) or in combination with barium (4/8). There was no overall preference for either room air (4/25) or CO₂ (9/25), with just fewer than half the respondents (12/25) believing that they are equally effective. Gas insufflation to patient tolerance (80%, 20/25) was preferred over volume- (0/25) or pressure- (5/25) limited methods. Most respondents (56%, 14/25) vary the rectal tube used according to the patient. All respondents (25/25) think that both prone and supine imaging is required, with most (81%, 21/26) believing that IV contrast material is not necessary. The routine use of spasmolytics is suggested by only 15% (4/26) of respondents. Forty-six percent (12/26) do not use spasmolytics in routine screening, whereas 38% (10/26) believe that spasmolytics should be used when patients experience pain, discomfort, or spasm. The largest acceptable slice thickness of 3 mm was agreed on by 88% (22/25) of respondents. All respondents believe that screening virtual colonoscopy should be performed at a lower dose than conventional CT, with most (58%, 15/26) believing that the tube current should be set at the lowest possible level to allow optimal visualization of the colonic wall even if visualization of parenchymal organs is severely reduced.

Interpretation.—Most respondents (80%, 20/25) believe that, at the current time, the optimum method of interpreting virtual colonoscopy should be primary axial review, with 3D used for problem solving. No consensus was apparent for determining the minimum requirement for interpretation of virtual colonoscopy images. Forty-four percent (11/25) believe that the minimum method is still primary 2D, with 3D for problem solving, 20% (5/25) believe that 2D cine alone is sufficient, 32% (8/25) believe that 2D with multiplanar reconstruction is sufficient, and one respondent believes that primary 3D review is required.

Reporting.—All but one respondent (96%, 26/27) believe that there is a threshold size below which polyps are not clinically important. When reporting virtual colonoscopy results, 59% (16/27) believe that polyps less than 4 mm do not need to be reported, and 52% (14/27) believe that polyps less than 5 mm do not need to be reported. However, 41% (11/27) believe that all potential polyps visualized should be reported. The decision of whether a polyp of a certain size detected by virtual colonoscopy should be removed by polypectomy or remain in place until the next screening interval remains an area of controversy. Slightly less than half (46%, 11/24) of respondents believe that polypectomy for polyps less than 10 mm detected on virtual colonoscopy should not be routinely recommended. The remainder of respondents believed that the threshold should be between 5 and 9 mm.

Consensus Statement
Role of virtual colonoscopy.—Virtual colonoscopy is currently a credible alternative screening method when performed by radiologists trained in and conversant with the technique and should be considered a reasonable alternative to the other colorectal cancer screening tests (e.g., barium enema and flexible sigmoidoscopy) when a patient is unable or unwilling to undergo conventional colonoscopy.

Technique.—Colonic cleansing remains necessary and is sufficient preparation without the need for fecal tagging. Either room air or CO₂ can be used, and the tube chosen should be individualized to the patient (e.g., balloon-tipped catheters for older patients with poor sphincter tone, flexible catheters for the young). The injection of IV contrast material is not necessary. Spasmolytics should not be routinely administered but can be used if patients experience pain, discomfort, or spasm. Scanning must be performed in both the prone and supine positions with a slice thickness of 3 mm or less, and the tube current must be set at the minimum level possible that allows adequate visualization of the colonic wall even if visualization of parenchymal organs is reduced.

Interpretation.—At the present time, the most commonly used platform for interpretation of virtual colonoscopy images is primary 2D interpretation, with 3D used for problem solving; however, primary 3D interpretation with 2D or multiplanar reconstruction for problem solving is acceptable and is even preferred by a minority of respondents.

Reporting.—There is a threshold size below which polyps are not clinically important. Lesions less than 5 mm that are detected on virtual colonoscopy may not need to be reported. However, a large minority of experts believes that all lesions should be reported regardless of size.

Discussion

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Many studies have documented the accuracy of virtual colonoscopy [1, 2], even with older CT scanners. New studies performed on MDCT scanners with experienced interpreters using proper CT and cleansing techniques have shown statistical equivalence with conventional colonoscopy [3, 4]. The challenge facing virtual colonoscopy today is to standardize the technique and develop a set of guidelines for its clinical implementation. The goal of this study was to develop a consensus opinion that can be used to guide clinical practice and future clinical trials. The importance of setting guidelines can be exemplified by the recent publication of the disappointing results of a multicenter trial [5]. The study showed some critical flaws that partially explain the poor sensitivity among several centers in the study. The CT technical parameters varied and methods of interpretation were not standardized. Perhaps the most critical flaw was the lack of training and experience by many of the interpreting radiologists. It is widely agreed that training is critical to the proper performance of virtual colonoscopy, and several major teaching institutions offer training programs in virtual colonoscopy. However, our survey did not address the necessary requirements or curriculum content of an appropriate training program. This issue is being addressed by a separate questionnaire survey of virtual colonoscopy experts to define the requirements and curriculum of an appropriate training program.

The proper role of virtual colonoscopy as a screening test is the most important issue to be addressed. The use of virtual colonoscopy can take several possible paths: it can be considered a third-tier test behind both conventional colonoscopy and double-contrast barium enema, a second-tier test to serve as a replacement for double-contrast barium enema, or a primary screening test competing directly with diagnostic conventional colonoscopy. The results of this survey show a growing consensus for the use of virtual colonoscopy as a primary screening test. This view was further supported by the recent publication of favorable virtual colonoscopy results in the New England Journal of Medicine [4] in a purely low-risk screening population.

Several studies [6–10] have evaluated the most appropriate use of CT parameters, stool cleansing regimens, contrast material, and spasmolytics. In the early development of virtual colonoscopy, a wide variety of protocols was used. Over time and with the development of MDCT, protocols used by various researchers and clinical practices have become more uniform. This developing uniformity is apparent in the results of the survey. All respondents agreed on a combination of prone and supine scanning, and most agreed on a minimum 3-mm collimation. Consensus was also apparent for the lack of need for routine use of spasmolytics and IV contrast material for screening virtual colonoscopy. However, no consensus was apparent regarding the use of CO₂ versus room air. The lack of consensus may reflect a combination of factors. Just fewer than half of respondents believed that CO₂ and room air are equally effective, but the questionnaire did not evaluate the two main qualities of effectiveness, degree of distention and patient comfort. When respondents expressed a preference, CO₂ was preferred. The main benefit of CO₂ is based on the absorption of the gas through the colonic wall, which is believed to result in improved patient comfort after the procedure. The benefits of room air are that it is readily available at no cost and requires no special equipment to deliver.

Multiple methods of interpretation of virtual colonoscopy have been proposed and evaluated [11–18]. As visualization techniques and computer-aided diagnostic strategies evolve, the preferred methods for interpretation will obviously undergo change. This survey was meant to characterize the current status of virtual colonoscopy interpretation and not to attempt to predict the future. Most respondents currently interpret virtual colonoscopy studies using a primary 2D approach, with 3D reserved for problem solving; however, a minority of respondents preferred a primary 3D approach. Currently, no direct studies have compared a modern primary 3D interpretation approach (such as that recently published [4]) with the primary 2D approach in the same patient population. Most studies to date have used the primary 2D interpretation method with success; in fact, success has been achieved with both approaches [1–4, 13, 15, 16]. However, the radiologists' choice of methodology for interpretation is likely to be based on user preference and experience. As vendors improve and modify the software available for virtual colonoscopy interpretation, market forces likely will drive vendors to provide platforms that over time will become similar in design and features.

As with any screening test, the goal is to maintain a sufficient sensitivity to promote disease prevention while maintaining a satisfactory specificity to prevent unnecessary followup examinations and potential patient harm. Methods of reporting play an important role in this regard. Similar effects have been seen in mammography and have led to a standardized reporting system known as BI-RADS (American College of Radiology Breast Imaging Reporting and Data System, trademark of the American College of Radiology; 2003). Such a system for virtual colonoscopy will likely be developed. Determining whether polyps below a certain threshold are clinically significant has been an area of much study and debate. However, because the concept of "advanced" or "dangerous" adenomas was introduced in 1992, less concern has been directed to the diminutive colorectal adenoma, and there is increasing evidence in the literature that one can safely follow up lesions less 1 cm. In the study by Hofstad et al. [19], the authors concluded that follow-up of unresected polyps up to 9 mm is safe. This conclusion was based on the fact that although polyps less than 5 mm showed a tendency to net growth, polyps 5–9 mm showed a tendency to net regression in size, both for adenomas and hyperplastic polyps [19]. In the study by Aldridge and Simson [20], the authors concluded,

Although severe dysplasia and malignancy do occur in adenomas less than 10 mm in size, they are rare in lesions of less than 5 mm. We recommend routine destruction of all polyps 5 mm or more in size, though it is not essential to remove those of less than 5 mm if they are kept under surveillance.

According to the results of our survey, virtual colonoscopy experts clearly believe that there is a threshold size of polyp below which polyps are not clinically important. Most believe that polyps less than 5 mm do not need to be reported because of the low likelihood of future malignancy in these lesions. A large minority (41%) believe that all polyps should be reported. When these respondents made comments to the consensus statement, the most common comment regarding the need to report small polyps pertained to the ability to follow up or locate the diminutive polyp on subsequent virtual colonoscopy studies rather than a concern for the potential to harbor malignancy. In virtual colonoscopy interpretation, lesions less than 5 mm, when true-positive, are more likely to be hyperplastic than adenoma; in addition, there will be a number of false-positive lesions representing adherent stool. Therefore, a lesion less than 5 mm is unlikely to be an adenoma. Even if the lesion were an adenoma, many would not recommend its removal, which is why many think that lesions less than 5 mm "may not need" to be reported.

The results of this study and the derived consensus statement provide a resource from which a set of guidelines and practice standards can be developed. The American College of Radiology Committee on Colon Cancer has been charged with developing a formal draft document, and this report has been submitted for reference (Glick S, personal communication).

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