This is a single-center observational feasibility study to evaluate the overall performance of the surgical navigation system during robotic surgery, without impact on the surgical procedure itself. The duration of this study will be approximately 2.5 years. Patients scheduled for a sentinel node procedure at the NKI are eligible for inclusion. Patients are informed about the study before the planned surgery and, after being provided with the necessary information regarding participation in the study, will be asked for informed consent. No additional risk is expected using the NDI navigation setup. Patients will receive some additional radiation due to the CT scan during surgery; a perioperative CBCT scan (~ 4 mSv) is acquired. This extra dose is low, considering other standard imaging in these patients like, pre-operative imaging with SPECT/CT scans. After surgery, no further participation or cooperation of the patient is required.

A patient-specific 3D model will be created using an available pre-operative SPECT/CT scan. Pre-operatively, three electromagnetic patient trackers will be attached to the patients' skin, close to the pelvis, allowing tracking the patient's position during surgery. After anesthesia and before the skin disinfection procedure, the patient is placed in the final surgical position, where an intra-operative CBCT scan is performed required for the image-guided surgery workflow. During surgery, the preoperative images and 3D model will be visible for the surgeon together with a blunt-tip electromagnetic pointer enabling surgical navigation during robotic surgery. Anatomical structures will be used to validate the accuracy of the navigation. When the target is identified by the surgeon, the pointer is used to store the location digitally. Scheduled standard clinical 99mTc will be used as validation for target(s) identification.

The percentage of successful image-guide assisted sentinel nodes removed, in which failure is defined as sentinel nodes which are per-operatively incorrectly identified as target SN by the navigation.

Evaluation of the usability of the image-guided navigation will be evaluated using the system usability scale (SUS). This scale ranges from 0-100 where a higher score means a better outcome.