Using Diffuse Reflectance Spectroscopy Probes to conduct Optical Measurements during Surgery for Colorectal Cancer

Differences in optical characteristics between malignant and benign tissue
allow for the discrimination between these tissue types. By performing Diffuse
Reflectance Spectroscopy (DRS) measurements at the planned resection plane
during surgery for colorectal cancer, a surgeon could better plan the most
optimal dissection plane, preventing a positive surgical margin. Lowering the
incidence of positive resection margins increases disease-free survival and
cancer-related survival. To use this technique in vivo during surgery for
colorectal cancers, several probes have been developed in-house. Because of the
limited space in the lower pelvis, the rigid pen-like Iris probe could maximize
the area of the rectum that can be reached. In contrast, the smaller drop-in
probe may make it easier to achieve optimal tissue contact in the deep pelvis
and to aim the probe tip precisely. In the first part of this study, we aim to
select the most suitable probe. In the second part, we will determine the
accuracy of the selected probe in rectal surgery for determining positive
resection margins.

To assess the practical usability of our DRS probes for the detection of
positive resection margins in colorectal cancer surgery - specifically whether
they can be used in the confined surgical workfield in the lower pelvis - as
well as the predictive properties for estimating malignancy at the site of
measurement.

During open resections of the rectum, after the TME plane has been developed
but before the transection of the rectum, DRS measurements will be taken. For
patients undergoing surgery for advanced colon cancer, pelvic recurrence of
rectal cancer or HIPEC procedure, the measurements will be performed when the
area of tumour tissue is approached. The study is divided in two distinct
phases. In the first phase, we will test 2 designs of the optical probe: a
blunt tip handheld pen-like probe (Iris probe) and a blunt tip *drop-in* probe.
The most suitable and intuitive optical probe will be selected, based on the
SUS score. To this end, patients will be spread across two groups,
corresponding with the two different probes to be tested. Measurements of the
first group of 9 patients will be obtained using the sterile, blunt tip,
hand-held DRS Iris probe as described in study N19BOR. Measurements of the
second group of 9 patients will be obtained using a sterile, blunt tip, drop-in
DRS probe as described in study N20DPP. The Iris probe has one efferent and six
afferent integrated optical fibres, which will be brought in contact with the
surface of the resection plane. The drop-in probe has one efferent and one
afferent fibre. The measured site will be marked peroperatively with sutures or
clips, which will be replaced by ink marking before pathology analysis. At the
end of the first phase, the most suitable and intuitive DRS probe will be
selected by assessing the SUS score of the surgeons. With this probe we will
continue the second phase of the study, aimed to determine the accuracy of this
probe to predict a tumor positive resection margin. The obtained DRS spectra
will be analysed using our machine learning algorithm, trained on earlier
measurements on ex vivo specimens. We expect that we do not need to train a new
algoritm, as we have extensive experience that ex vivo measurments are
comparable to in vivo tissue measurments with regard to DRS. For validation we
will use the gold standard pathology results on resection margin status.

No significant risks are expected; maximum of 5 minutes added to operation
time.