Surgical Procedure
Preoperatively, the near-infrared (NIR) fluorescence camera (Quest Spectrum 2.0, Quest Medical Imaging, the Netherlands) was used to investigate whether the SLN was detectable transcutaneously. During the operation, detection of SLNs was first assessed using a near-infrared (NIR) fluorescence camera, after which the handheld gamma probe (EuroProbe 3.2; PI-Medical, the Netherlands) was used for radioactive detection of SLNs. All lights in the operating room were dimmed and windows closed when acquiring the fluorescent images to reduce background signal. NIR images were taken with different exposure times (auto exposure, 25 ms, 50 ms, 100 ms) to capture the most optimal TBR. The wound bed was controlled for residual fluorescent or radioactive signal after SLN excision according to the same procedure as described for SLN detection. If residual signal was present, the surgeon searched for a second SLN. If no SLN could be detected by use of the gamma probe and NIR fluorescence camera, the surgeon could opt for the additional use of a peritumoral injection with blue dye.