Report in English with a Dutch summary (KCE reports 45A)

KCE reports vol.45 Screening for Colorectal Cancer 87
by examining those who had undergone a prior colonoscopic polypectomy345. In
this study the DCBE was less sensitive in detecting adenomas than colonoscopy
and the sensitivity was associated with the size of the adenomas. This finding
was confirmed by other studies194, 386.
Johnson et al. 386 compared relative sensitivity and specificity of CT colonography
with DCBE for the detection of colorectal polyps in a population reflective of a
screening setting. In addition the potentially added value of double reading at
CT colonography was assessed, using endoscopy as the gold standard . This
prospective, blinded study comprised 837 asymptomatic persons at higher than
average risk for colorectal cancer who underwent CT colonography followed
by same-day DCBE. Examinations with polyps 5 mm in diameter were
referred to colonoscopy. CT colonography readers detected 56% - 79% of
polyps 10 mm in diameter. In comparison, the sensitivity with DCBE varied
between 39% and 56% for the 31 polyps 10 mm. All of the readers detected
more polyps at CT colonography than DCBE, but the difference was statistically
significant for only a single reader (p = 0,02). Relative specificity for polyps 10
mm on a per-patient basis ranged from 96% to 99% at CT colonography, and
99%-100% at DCBE. Double-read CT colonography detected significantly more
polyps than DCBE (81% vs. 45% for polyps 1 cm (p 0,01), and 72% vs. 44%
for polyps 5 - 9 mm (p 0,01)). The authors concluded that double-read CT
colonography is significantly more sensitive in detecting polyps than single-read
DCBE.
5.5.7 Virtual colonoscopy
Virtual colonoscopy is a rapidly evolving technology under evaluation as a new
method of screening for colorectal cancer. However, up to today there have
been no published RCTs on the efficacy of virtual colonoscopy as a screening
strategy for CRC and its performance in this field has not yet been studied in
typical screening populations387, 328, 219.
The Blue Cross and Blue Shield Technology Evaluation Center report, Volume
10, nr. 6 387 rightfully underlines that there are many possible methods used in
the literature to analyze the diagnostic performance of CT colonography. The 2
most common methods are referred to as a per-polyp analysis and a per-patient
analysis. In the per-polyp analysis, the capability of CT to detect all polyps is
calculated in terms of sensitivity relative to a reference standard. Specificity
cannot be calculated because there is no real denominator for the absence of a
polyp. Although a per-polyp analysis gives some insight regarding the technical
capability of CT, it is not as relevant as a per-patient analysis in determining its
clinical utility. Furthermore, in most studies, the per-polyp analysis gives a
misleading estimate of sensitivity as it would be used clinically. The studies
usually consider CT colonography to have matched a polyp seen on
colonoscopy if the size of the polyp seen on CT is within 50% of the size
determined on colonoscopy. For example, a polyp measured as 5 mm on CT is
considered a positive finding for a polyp measured as 10 mm on colonoscopy.
However, this should not be considered as a positive finding in a per-patient
analysis, because to allow a 5 mm size threshold to be a positive test for
detecting 10 mm polyps would require such a threshold to be also applied to
the assessment of specificity. Thus, all patients who are accurately identified as
having only 5 mm polyps with CT colonography should be counted as false
positive if one requires a 5 mm threshold to identify a 10 mm polyp. Although
CT colonography is considered to be more sensitive for large polyps, clinically
this greater sensitivity may not bear out because the interpretation must not
only identify a large polyp, but also correctly classify it as a large polyp. Thus,