Contribution of SPECT/CT imaging to radioguided sentinel lymph node biopsy in breast cancer, melanoma, and other solid cancers: from "open and see" to "see and open".

A few years ago SPECT/CT was successfully incorporated into the sentinel node (SN) procedure for breast cancer and melanoma. Important contributions of SPECT/CT in these two malignancies were the anatomical localization of SNs already visualized on planar images, the detection of additional SNs in aberrant basins, and the depiction of SNs in cases with no visualization on planar images. Recently, in a large series of melanoma patients the use of SPECT/CT was associated with the detection of more metastatic SNs and a higher rate of disease-free survival. Following the experiences in breast cancer and melanoma, SPECT/CT has been applied in oral cavity cancer as well as in urological and gynaecological malignancies. In the areas of lymphatic drainage of these malignancies (head and neck, pelvis, and upper abdomen) SPECT/CT appears to be essential to localize SNs, providing surgeons with helpful anatomical landmarks to plan SN biopsies. In gastrointestinal and lung malignancies SPECT/CT has only incidentally been used. With the improvement of the CT component in the second generation of SPECT/CT gamma cameras, nuclear physicians today can identify lymph nodes corresponding with the radioactive SNs. This is possible using a display of SPECT/CT similar to that of conventional tomography. Multiplanar reconstruction enables to correlate radioactive sentinel nodes seen on fused SPECT/CT with lymph nodes seen on CT, and the use of cross-reference lines allows the navigation between axial, coronal and sagittal views. This visual information is helpful for the intraoperative procedure and for post-excision assessment using portable devices. Fused SPECT/CT images may also be three-dimensionally displayed, improving anatomical SN localisation and recognition. This recent imaging improvement is leading to a new paradigm of "see and open" in contraposition to the former "open and see" in the SN procedure. The new mixed reality protocols which are able to transfer SPECT/CT to the operating room for surgical navigation will reinforce this "see and open" concept. However, a comprehensive interpretation of SPECT/CT together with lymphoscintigraphy is necessary to identify radioactive lymph nodes as sentinel nodes and classify them into different categories that are important for the intraoperative procedure.