Polyp size measurement during real-time colonoscopy using the virtual scale function SCALE EYE: variability and systematic differences

Polyp size plays an important role in early detection and prevention of
colorectal cancer (CRC). First of all, since the size of polyps at index
colonoscopy contribute to the estimated risk of future CRC, endoscopic
measurement of polyp size is important for deciding on appropriate surveillance
intervals. For example, most international guidelines advise a 3-year
surveillance interval for individuals diagnosed with lesions >= 10mm and 5 or
10-year intervals for smaller polyps. Besides this 10 mm cut-off, polyp size is
also correlated with the chance that a lesion harbors invasive growth (higher
chances of invasive growth with increasing polyp size). As such, size also
affects the choice of treatment modality for polypectomy. Last but not least,
polyp size is essential for safe implementation of an optical diagnosis
strategy, in which 1- to 5-mm polyps are characterized during endoscopy and
resected and discarded without histopathological analysis (no guidelines are
available for larger polyps yet).

Although assessment of polyp size is important for clinical decision making, no
reference standard is available. In daily practice, polyp size is assessed
visually by endoscopists (*carpenters eye*) or with instruments of known size
adjacent to the lesion as a visual reference. Hence, polyp size measurment is a
mostly intuitive and subjective proces, prone to inter-observer variability. In
addition, although measurement of polyps using uncalibrated devices of known
size might improve realiabilty, measurement is usually performed without
additional disposable devices, because it leads to prolonged examination times
and increased costs.

Recently, Fujifilm has developed a new real-time virtual scale functionality to
their endoscopy system, known as *SCALE EYE*. SCALE EYE is developed to assist
endoscopists in measuring polyp size during colonoscopy. This function makes
use of a built-in laser and an image processing technology. As such, no
additional disposable devices are required. When a polyp is detected, the
endoscopist can switch on a red laser and the virtual scale (displayed on the
monitor screen) of the SCALE EYE functionality by pressing a button on the
handle of the endoscope. When the image sensor of the endoscope detects the
laser dot and the laser dot is correctly positioned on the left border of the
polyp, the polyp size within the image can be measured in real-time using the
virtual scale. We hypothesize that SCALE EYE can aid to make polyp size
measurment more objective, and hence reduce inter-observer variability.

1. To assess the variability (spread) and systematic differences in polyp size
measurement between SCALE EYE and several other measurement techniques (without
reference [i.e. 'carpenters eye'], opened snare (of known size) as reference,
pathologist assessment).
2. To assess the time-efficacy and user satisfaction of the SCALE EYE polyp
size measurement during colonoscopy.

The study is designed as a single center prospective observational study. We
will compare polyp size measurements using SCALE EYE with several other polyp
size measurement techniques: size measurements by endoscopist without a
reference (*carpenters eye*) , size measurements by endoscopist with an opened
snare (of known size) as a reference and size measurements by the pathologist
during histopathological analysis.

During screening colonoscopies, detected polyps (maximum of four per
colonoscopy) will be measured using all three different colonoscopy measurement
techniques. This will be done by experienced endoscopists (i.e. endoscopist
accredited for colonoscopies within the national CRC screening program). The
colonoscopy will be videotaped and subsequently digitally stored. Video
recording extracts of the polyp size measurements will later be presented to
eight expert endoscopists and four to eight fellows (depending on
availability). They will estimate polyp size by all three different endoscopic
measurement techniques (i.e. based on the video recording extracts).
Histopathological analysis and size measurements of the resected polyps will be
performed by pathologists with expertise in gastrointestinal pathology.
Variability and systematic differences in polyp size measurement between these
four measurements will be assessed.

Possible risks accompanied with the procedure are similar to that of regular
colonoscopy procedures. These risks comprehend, among others, a small risk for
colorectal bleeding (~1.5%) or perforation (~0.1%). Usage of the SCALE EYE
functionality and performance of additional measurements does not cause
additional risks. However, the additional measurements might cause short
lengthening of the procedure (to an esimation an average of 5 additional
minutes).