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«PacifiCare’s medical management guidelines represent the recommendation of the PacifiCare Medical Management Guideline (MMG) committee. They are ...»

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Regulatory Requirements Food and Drug Administration (FDA): Helical CT scanners are regulated by the FDA as Class II devices, and numerous systems have met all requirements of the 510(k) approval process. The complete list of commercially available helical CT scanners is too extensive for inclusion here; however, major manufacturers of devices used in the studies selected for detailed review include Siemens Medical Solutions, General Electric Medical Systems, and Philips Medical Systems.

Additional information may be obtained directly from the Food and Drug Administration (FDA) [Website] - Center for Devices and Radilogical Health (CDRH) at: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMN/PMN.cfm.

Accessed March 19, 2009.

Research Evidence Background Colorectal cancer is the third leading cause of cancer deaths in the United States. When polyps are identified and excised before cancerous change and when colon cancer is identified when it is still localized, it is highly curable. However, widespread or metastatic colon cancer is difficult to treat successfully. Therefore, early identification is the most effective strategy to reduce mortality from colon cancer. Colonoscopy is the "gold standard" screening test; however, it is invasive and frequently requires sedation or anesthesia, so screening rates are low.

Computed tomography colonography (CTC), also referred to as virtual colonoscopy, is a less invasive method of colon cancer screening that has been developed to obtain detailed 2-dimensional (2D) and 3-dimensional (3D) colonoscopic images of the colon and rectum using helical computed tomography (CT). These images are then reconstructed to produce computer-generated 3D images suitable for interpretation by a gastrointestinal radiologist. If suspicious lesions are detected, the patient usually undergoes further testing, including possible biopsy, by conventional colonoscopy. Since CTC is less invasive than conventional colonoscopy and does not require sedation, it may be more acceptable to patients and thereby improve compliance with colorectal cancer screening recommendations.

Computed Tomographic Colonography - Commercial Medical Management Guideline

Research Screening Twelve studies published between the years 2003 to 2005 met the criteria for detailed review. These included nine prospective, evaluator-blinded studies and three meta-analyses. All but one of the prospective studies compared computed tomographic colonography (CTC) with conventional colonoscopy alone. One study assessed the comparative accuracy of three screening tests: CTC, colonoscopy, and air-contrast barium enema (ACBE) (Rockey, 2005). Many of the studies used conventional colonoscopy as the reference standard; several of the studies used segmental unblinding to create an enhanced reference standard; one study used a combination of the initial findings of conventional colonoscopy, any additional findings after segmental unblinding to CTC reports, and the results of additional diagnostic tests performed at a later time.

The Rockey et al. study, which used segmental unblinding during the colonoscopy, developed a consensus view of the colon after reconciling all three colon screening tests (ACBE, CTC, and colonoscopy); that is, the reference standard was the combined dataset for all three colon studies rather than for the colonoscopy itself. In all of the studies, CTC images were evaluated independently by one or more radiologists who were blinded to the indications for and results of colonoscopy, and conventional colonoscopy was performed by gastroenterologists blinded to the results of CTC.

However, in those studies that used segmental unblinding, if a lesion was noted on CTC but not on conventional colonoscopy, the endoscopist tried to confirm it by a second look after segmental unblinding. The terms polyp and lesion are used interchangeably in this report.

Hur et al. reviewed decision-analytic techniques to compare the outcomes of 2 management strategies for smaller (6-9 mm) polyps discovered by CTC (Hur, 2007). Hypothetic average-risk patients who had undergone a CTC examination and found to have a small (6-9 mm) polyp were simulated to either: (1) undergo immediate colonoscopy for polypectomy (COLO), or (2) wait 3 years for a repeat CTC examination (WAIT). The COLO strategy resulted in 14 total deaths per 100,000 patients compared with 79 total deaths in the WAIT strategy, for a difference of 65 deaths. The COLO strategy resulted in 39 cancers per 100,000 patients vs. 773 in the WAIT strategy, for a difference of 734 cancers. The authors concluded that managing smaller polyps detected on a screening CTC with another CTC examination 3 years later likely will result in more deaths and cancers than immediate colonoscopy and polypectomy.

Kim et al. compared primary CTC in 3120 consecutive adults with primary optical colonoscopy (OC) screening in 3163 consecutive adults (Kim, 2007). The main outcome measures included detection of advanced neoplasia (advanced adenomas and carcinomas) and total number of harvested polyps. Primary CTC and OC screening resulted in similar detection rates for advanced neoplasia (3.2% for CTC and 3.4% for OC), although the numbers of polypectomies (561 CTC vs. 2434 OC) and complications were considerable smaller (7 colonic perforations in the OC group vs. none in the CTC group) in the CTC group. The authors therefore concluded that these findings support the use of CTC as a primary screening test before therapeutic OC.

Polyps/Colorectal Cancer Some studies were conducted in low-prevalence populations consisting of asymptomatic adults at average risk for colorectal cancer, as well as in asymptomatic patients with increased risk for colorectal cancer. Those at average risk generally were referred for routine, clinically indicated colonoscopy. Other studies were conducted in symptomatic patients (e.g., as a follow-up to an abnormal screening test, such as hemoccult testing, sigmoidoscopy, or barium enema, or to evaluate iron deficiency anemia or minor gastrointestinal symptoms), and/or in individuals with a personal or family history of colorectal polyps or cancer. Sample sizes for the prospective studies ranged from moderate (n=150 to n=250, 4 studies), to large (n=600 to n=703, 3 studies), to very large (n=1233, 1 study). One meta-analysis analyzed data from 1324 participants in 14 prospective studies (Sosna, 2003); 1 included data from 4181 patients from 24 studies (Halligan, 2005), and the third meta-analysis included 33 prospective studies involving 6393 patients (Mulhall, 2005). Inclusion criteria for the meta-analyses were similar: prospective, blinded studies of adults undergoing CTC after full bowel preparation, with colonoscopy (or surgery for the Mulhall et al. analysis) as the reference standard; use of state of-the art

Computed Tomographic Colonography - Commercial Medical Management Guideline

technology, including at least a single-detector CT scanner with supine and prone positioning, and both 2-dimensional and 3-dimensional views during scan interpretation. The Sosna et al. analysis included 7 studies with 50 patients (50%) and 4 studies with 50 to 100 patients (28.6%). The Halligan et al. analysis included 4 studies with 50 patients (16.7%) and 10 studies with 50 to 100 patients (41.7%). The Mulhall et al. analysis included 3 studies with 50 patients (9.1%) and 12 studies with 50 to 100 patients (36.4%).

As in the earlier studies, the principal outcome measures were sensitivity and specificity of CTC on a per-patient and perlesion basis. Some investigators noted that the per-patient data provided the most important perspective for a screening test since this analysis assessed the ability of CTC to identify patients with colorectal lesions who are in need of a colonoscopy, excluding those without clinically relevant lesions who do not need to undergo colonoscopy. Per-polyp data emphasized the ability of CTC to find colonic lesions, i.e. this type of analysis assessed the performance of the technology rather than its utility as a screening tool (Halligan, 2005; Mulhall, 2005). Some studies provided results for all types of polyps combined (neoplastic and non-neoplastic), whereas other studies distinguished between neoplastic polyps (adenomas or adenomatous polyps) and non-neoplastic polyps (hyperplastic polyps) that do not have the potential to become cancerous. Some studies used the term lesions rather than polyps to include carcinomas as well as adenomas.

Findings from these studies suggest that the sensitivity of CTC on a per-polyp basis is dependent on lesion size, with sensitivity increasing with increasing size of the lesion. In the individual studies, sensitivity for lesions 10 mm in diameter or larger ranged from 51% to 100%, with a median of 76%. The Sosna et al. meta-analysis reported pooled perpolyp sensitivities of 81% for polyps greater than or equal to 10 mm and 43% for polyps less than or equal to 5 mm, with a significant increase in sensitivity for detection of polyps increasing as the polyp size increased. In two of the smaller studies that investigated overall sensitivity (for any size lesion), values were reported to be 70% and 64% for polyps, and 72% for neoplastic polyps. (Iannaccone, 2003; Iannaccone, 2004) Per-patient sensitivity for lesions greater than or equal to 10 mm in diameter ranged from 52% to 94% with a median of 72%. Some, but not all, studies showed an increase in sensitivity with an increase in size of the lesion. The Sosna et al.

meta-analysis reported pooled per-patient sensitivities of 88% for polyps greater than or equal to 10 mm and 65% for polyps less than or equal to 5 mm. The Halligan et al. meta-analysis indicated per-patient mean sensitivity of 93% for CTC in patients with large polyps (greater than or equal to 10 mm) with a decrease in sensitivity to 86% when patients with medium-sized polyps (6-9 mm) were included. The larger meta-analysis by Mulhall et al. reported pooled perpatient sensitivities of 85% for polyps 9 mm (range 48% to 100%) and 48% for polyps 6 mm (range 14% to 86%), with an overall sensitivity of 70% (range 21% to 96%). Four individual studies reported overall per-patient sensitivity ranging from 62% to 96%.

Overall, per-patient specificity was not quite as dependent on polyp size with some studies showing an increase in specificity with increasing size of lesion, while others did not. Specificity for lesions greater than or equal to 10 mm in diameter ranged from 92% to 97%, with a median of 95.5%. The Sosna et al. meta-analysis reported a 95% pooled overall specificity for detecting polyps 10 mm, Halligan et al. reported a per-patient mean specificity of 97% for lesions greater than or equal to 10 mm and an 86% specificity for lesions 6-9 mm in diameter and Mulhall et al. reported a perpatient specificity of 97% for polyps 9 mm and 91% for polyps 6 mm. In three studies that reported per-patient specificity for lesions greater than or equal to 6 mm, values were 70%, 80%, and 83%, respectively. Finally, in five studies that reported overall (for any size lesion) specificity, the values were 31%, 62%, 71%, 92%, and 97%, respectively. In the study that reported the lowest overall specificity, 83% of polyps were Results of three large, well-designed studies conducted during the same time period and in similar patient populations were inconsistent: two reported negative findings, while one reported positive results. Johnson et al. reported that in a low-prevalence setting consisting of 703 asymptomatic patients at higher-than-average risk for colorectal cancer, polyp detection rates of CTC were well below those at colonoscopy (Johnson, 2003). Sensitivity rates were less than previous reports, based largely on cohorts with high lesion prevalence. For polyps greater than or equal to 10 mm, average (of

Computed Tomographic Colonography - Commercial Medical Management Guideline

three readers) per-polyp sensitivity was 50.7% and average per-patient sensitivity was 52.3%. There was high interobserver variability, which the investigators suggested may be due to the low prevalence of polyps in this cohort and the high impact on total sensitivity of each missed polyp. However, per-patient specificity, which was based on high numbers, was high and showed excellent agreement among observers.

In contrast, the Pickhardt et al. study, conducted in a low prevalence, asymptomatic, average-risk screening population (n=1233), reported that CTC was an accurate screening method and compared favorably with optical colonoscopy in terms of detection of clinically relevant lesions (Pickhardt, 2003). CTC had a high sensitivity (89% per-patient, 86% perpolyp) and an acceptable specificity (80% per-patient) for adenomas that were greater than or equal to 6 mm in diameter.

For polyps greater than or equal to 10 mm, the per-patient sensitivity was 94% (compared with 88% for colonoscopy).

There were some notable differences between the two studies.

The Pickhardt et al. study was one of the first to use segmental unblinding (the Johnson et al. study did not), and presented data only for adenomatous polyps, while the Johnson et al. study combined data on all types of polyps. The Pickhardt et al. study used some technological advances that were not generally available at the time, such as electronic cleansing (with stool tagging and electronic subtraction), and interpretation of imaging that relied primarily on a 3dimensional, rather than 2-dimensional, approach for the detection of polyps. The third study, conducted by Cotton et al.

at nine major hospital centers, consisted of a largely average-risk population of 615 participants who were referred for routine and clinically indicated colonoscopy, and reported that CTC was not ready for routine use at this time (Cotton, 2004). The primary outcome measure, sensitivity of CTC for the detection of patients with lesions greater than or equal to 6 mm, was only 39% and was not much higher (55%) using a threshold of at least 10 mm. Unlike the Pickhardt et al.

study, this study did not use stool tagging or 3-dimensional rendering as a primary review. Also, thicker lower resolution CT section collimation was used at some sites. This study actually began 2 years before the Pickhardt et al. study and older technology was used. In addition to possibly outdated technology, another limitation of this study was the inexperience of some of the radiologists.

The meta-analyses also arrived at different conclusions. The earlier and smaller of the three reports by Sosna et al.

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