Introduction

Since its introduction (in 1994) [1], clinical implementation of computed tomography (CT) colonography has been governed by advances in CT technology, improvements in dedicated analysis software, development of patient preparation regimens and local diagnostic policies.

In 2007 the European Society of Gastrointestinal and Abdominal Radiology (ESGAR) consensus statement on CT colonography was published, detailing how best to conduct and interpret the examination [2]. That document was based on collective experience up to the beginning of 2006, and the authors represented the EU countries in which CTC underwent consistent clinical implementation (UK, Italy, Belgium and The Netherlands). Over the last 5 years expansion of the CT colonography literature has continued and several important studies, including multicentre studies, have been published [3–5]. These new data have provided further insight regarding optimisation of the CT colonography technique, interpretation and diagnostic capabilities. Indeed CT colonography is now recommended for colorectal cancer screening by several international groupings and is widely used to investigate patients with symptoms suggestive of colorectal cancer [6, 7]. Although recent review articles provide some guidance regarding the optimal CT colonography technique, given the evolving data [8–11] there is a current need to update the ESGAR consensus document.

The purpose of this article is therefore to update quality standards for CT colonography based on examination of the existing literature and expert opinion from key opinion-leaders within the European Society of Gastrointestinal and Abdominal Radiology.

Materials and methods

Consensus panel

A multinational European panel of nine members of the ESGAR CTC Working Group (comprising J.S., S.H., S.T., P.L., T.M., D.R., M.H., A.L., E.N., and representing six EU countries: Austria, Belgium, Italy, The Netherlands, Sweden and the UK) used a modified Delphi process [12, 13]. The Delphi process consists of a survey conducted in two or more rounds; the answers (or statements) collected in the first survey are modified in the second, the third, etc., to reach the maximum consensus among the experts. We rated the level of agreement among the experts on a variety of statements pertaining to the acquisition, interpretation and implementation of CT colonography. Four Delphi rounds were conducted, each at 2 months interval.

One of the panellists was chosen as the facilitator (E.N.).

In the first round the facilitator emailed a questionnaire with 22 items pertaining to panel members’ personal approaches to CTC, including items on patient preparation, data acquisition technique, image interpretation and clinical implementation (Table 1). Responses collected from all panellists were merged into a unique datasheet that served to identify areas of agreement and conflict in panellist opinion.

Table 1 Second ESGAR CT colonography consensus. Survey of the first Delphi round
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In the second round, the panellists attended a 1-day, face-to-face meeting, and, on the basis of their main areas of research and expertise, were divided into four working groups (WG) as follows: bowel preparation and tagging (WG 1), insufflation and scanning protocols (WG 2), reading paradigm (WG 3) and reporting (WG 4). Each WG independently drafted a cluster of statements pertaining to their allocated subject (Table 2). Each statement was built on the basis of panelists’ expertise and available indexed literature. Each WG then presented their proposed statements to the whole panel for consideration and subsequent discussion, during which time the content and wording of statements were modified until a general consensus emerged.

Table 2 Statements elaborated by the panellists in the second Delphi round, and discussed in the third and fourth to reach the maximum consensus and Cronbach's internal reliability. Statements with score between 4 and 5 are highlighted to show the situations in which all panellists agreed on the statement but the level of support differed (i.e. “agree somewhat” versus “agree strongly”)
Full size table

In the third and fourth rounds, copies of the latest statements were sent by email to panellists, who then indicated independently their level of agreement with each individual statement using a 5-point scale, as follows: 1, strongly disagree with the statement; 2, disagree somewhat with the statement; 3, undecided; 4, agree somewhat with the statement; 5, strongly agree with the statement.

After the third round the facilitator collected panellists’ ratings and determined the agreement score for each statement. If the mean score for an individual item was lower than four (maximum possible = five) the facilitator asked panelists to review the statement and attempt to reach a consensus in the fourth round.

Statistical analysis

To measure the internal consistency of panellist’s ratings for each statement, a quality analysis was performed using Cronbach's α correlation coefficient and SPSS (SPSS, Chicago, Ill.) [14]. Cronbach's α was determined after each round.

Cronbach’s α reliability coefficient normally ranges between 0 and 1. The closer the Cronbach’s α coefficient is to 1.0, the greater the internal consistency of the item. An α coefficient > 0.9 was considered excellent, α > 0.8 good, α > 0.7 acceptable, α > 0.6 questionable, α > 0.5 poor and α < 0.5 unacceptable. For the iterations, an α of 0.8 was considered a reasonable goal for internal reliability. All panellist ratings for each statement were also analysed with descriptive statistics, estimating the mean, maximum and minimum score, and their standard deviation.

A mean score of 4 was considered to represent “good” agreement between panellists, a score of 5 “complete” agreement.

Results

Based on the questionnaire provided by the facilitator, the panel elaborated 86 statements that were collected by the facilitator and organised into nine groups, as follows: (1) rectal tube, (2) spasmolytics, (3) colon distension, (4) image acquisition, (5) patient preparation, (6) faecal tagging, (7) reading paradigm, (8) lesion measurement and (9) reporting (Table 2).

In the third round the panelists achieved complete consensus (i.e. mean score 5) in 64 of 86 statements (75 %), which improved to 71 (82 %) in the fourth round (Table 2).

Categories including the highest proportion of statements achieving excellent internal reliability (i.e. Cronbach's α value >0.7) in the final round were colon distension, scan parameters, use of intravenous contrast medium, general guidelines on patient preparation, role of CAD and lesion measurement.

Lower internal reliability was achieved for statements regarding the use of a rectal tube, spasmolytics, decubitus positioning and number of CT data acquisitions, faecal tagging, 2D vs. 3D reading and reporting. However, in the last round, no panellist scored their individual statements as less than 4 on the 5-point rating scale. This indicates that all panellists agreed on the statement but the level of support differed (i.e. “agree somewhat” versus “agree strongly”).

Discussion

Full consensus was reached by our expert panel in 82 % of the statements. In the remaining statements, full consensus was not reached but all panellists achieved a “good” level of agreement. In total, the panellists completed fours rounds; the first and second rounds served to elaborate the basic statements. The third and fourth rounds contained the core of the discussion and were necessary to reach the maximum consensus possible, so creating an optimised, homogeneous opinion for each statement.

All panellists exhibited a high level of agreement for the technical performance of CTC, with clear recommendations regarding colon distension, CT parameters, use of intravenous contrast agents and patient preparation. Full agreement was also reached regarding the role of CAD and lesion measurement. These data reflect a general homogeneity of approach between panel members despite their wide geographical spread. All panel members are regular tutors on the ESGAR CTC course, which may have increased their level of agreement; there is a tendency to promote a common message during panel discussions occurring during the ESGAR CTC courses [15, 16]. Furthermore, in these areas the indexed literature is relatively mature and stable; for example available data supporting the use of automated CO2 for optimal colonic distension is relatively consistent [17–20].

However, certain aspects of practice achieved less than “full” agreement. In particular, a digital rectal examination, before insertion of the rectal tube (if rectal examination had not been performed previously), was not standard practice in many centres, but was nevertheless recommended by some panellists (with a mean score 4.56). This difference could be explained by the practice to perform a digital rectal examination before CTC amongst a few of the experts involved in the consensus. Similarly, practice differed regarding the use of intravenous spasmolytics, with many administering such agents to all patients, whereas some (in Italy) only used it in selected individuals [21, 22]. Accordingly, use of spasmolytics is recommended by the majority but is not considered mandatory.

There were minor variations in recommended CT parameters between panellists but all recommended data acquistion in at least two patient positions, without any overall preference regarding the order of acquisitions (i.e. supine or prone first). The differences in CT protocols included the need for additional CT data acquisition and insufflation in cases of poor colonic distension; a minority of experts did not consider this mandatory although they agreed it should be recommended. An additional decubitus acquisition was recommended, if required, to improve the diagnostic quality of the examination [23, 24].

Although available CT technology differed among panellists, all agreed that 2.5-mm collimation was the maximum permissible (although thinner collimation is recommended when available) and use of low radiation dose protocols is to be employed when the overriding purpose of the study is the evaluation of the colonic lumen, for example as in screening [25, 26]. A low radiation dose should be considered a study in which the median effective dose is lower than 5.7 mSv, according to the results of the survey by Leidenbaum et al. [26]. For the staging of patients with known malignancy all the panellists agreed upon the use of standard-dose protocols and intravenous contrast medium [27, 28].

Substantial agreement was reached between panelists regarding the reading methods for interpretation of CT colonography. A combination of 2D and 3D reading was emphasised. Most of the panel were primary 2D readers but all recognised the importance of 3D integration, noting the range of different three-dimensional approaches available. The need for the reader to be adequately trained before interpreting CT colonography was emphasised and is strongly supported by the indexed literature [29–33].

Computer-aided diagnosis was acknowledged by all panellists as a potentially useful tool for CTC interpretation, if employed in a second reader paradigm. Accordingly, the use of CAD was recommended provided that readers have already undergone adequate training in general CT colonography interpretation so that they can discriminate between true- and false-positive CAD marks appropriately [34–42].

Panellists acknowledged that accurate polyp measurement is problematic for both CTC and endoscopy, with some evidence that CTC may be the superior technique [43, 44]. Despite this advantage, it is still uncertain whether a 2D or a 3D measurement should be made from CT. Moreover, the accuracy of such measurements has important clinical implications for the correct classification and risk stratification of lesions, influencing subsequent recommendations for patient management [45–50]. The panel concluded that the maximal diameter of lesions should be primarily estimated using axial and MPR 2D views (which were considered to be the most reliable), avoiding a narrow CT window. Some caution should be exercised when measurements are taken using 3D perspectives given the potential for distortion generated by the three-dimensional endoluminal rendering [51–55].

All panellists agreed that CTC should only be reported by a radiologist, and then only after adequate training [56–59]. Motivations behind this recommendation are mainly the medico-legal implications of non-radiologists reporting CTC in EU countries. In all EU countries the radiological report is definitively validated by the radiologist despite, in a few centres, a preliminary reading being performed by a radiographer. Adequate training means having interpreted a minimum amount of colonoscopy-verified cases. Although the precise number has not yet been clearly defined, the literature shows that 175 is even not sufficient for several individuals [60, 61].

It was acknowledged that diagnostic accuracy is lower for polyps with a maximal diameter less than 6 mm [3, 4] but if detected with high confidence, and particularly if more than three in number, such polyps should still be reported. This contrasts with recommendations from the CT Colonography Reporting and Data System (C-RADS), authored by Zalis et al., where lesions less than 6 mm are considered diminutive and the recommendation is that they should not be reported [45]. The panel agreed that the patient’s risk (age, family history of colorectal cancer, previous polypectomy, etc.), as well as the number of diminutive lesions detected, should be considered in the decision to report them or not.

There was little disagreement between panellists regarding the need to calibrate the laxative effect of bowel preparation/purgation to the individual patient and potential target lesion. All panellists agreed that faecal tagging should be used routinely. Different preferences for specific laxative and tagging agents were expressed (for example sodium phosphate, magnesium citrate, polyethylene glycol for cleansing, and barium, iodine or a combination of both agents for tagging), reflecting local practice [62–75].

In summary, the panel covered all important aspects regarding the practice of CTC and reached full agreement on most statements. The Consensus has been structured to give clear guidelines for the practice of CT colonography. The recommendations should be useful for both the radiologist who is starting a CTC service and for those who have already implemented the technique but whose practice may need updating in the light of recent developments.