**4. Technique of sentinel lymph node biopsy**

There is marked heterogeneity in the published data assessing the role of SLNB in OCSCC including preoperative investigations, technique of identifying the SLN and the pathological assessment of the specimens [16]. The GETTEC (Groupe d'Etude des Tumeurs de la Tête et du Cou) guidelines [17] have attempted to standardise the technique in performing SLNB with recommendations for lymphoscintigraphy, surgery and pathological analysis. Of note, they recommend a median of three SLNs to be sampled, with a single SLN node considered insufficient to accurately determine the nodal pathological status.

SLNB for OCSCC presents unique challenges in relation to both the complex anatomy of the head and neck, in addition to the short distance between the primary lesion and the draining nodal basin, particularly for lesions located in the floor of mouth. This is due to the high activity at the adjacent injection site, which can be easily overlooked by planar lymphoscintigraphy and intraoperative gamma probes [18]. Intraoperatively, the close relationship between the primary lesion and the draining lymph nodes can result in so called 'shine through' of the radioactive tracer from the primary site with difficulties in identifying the SLN if it is in an adjacent nodal basin, particularly the submental (IA) and submandibular (IB) basins. Composite single photon emission computed tomography (SPECT) with concurrent CT combines functional and anatomical imaging to enhance topographic orientation and diagnostic sensitivity, with more SLNs being detectable than by planar lymphoscintigraphy alone, as well as providing more detailed anatomical information to assist with intraoperative localisation [19]. **Figures 2** and **3** demonstrates the lymphoscintigraphy result and composite SPECT/CT for patients with unilateral and bilateral lymphatic drainage respectively. The SPECT/CT provides detailed anatomical information to assist with identification of the SLN.

Another consideration that may impact on the accuracy of lymphoscintigraphy is the choice of radiotracer. These have different molecular characteristics as

#### **Figure 2.**

*Lymphoscintigraphy and SPECT/CT demonstrating ipsilateral level 2 sentinel lymph node.*

#### **Figure 3.**

*Lymphoscintigraphy and SPECT/CT demonstrating bilateral drainage from a lateralised tumour.*

summarised in **Table 1**, which impacts the drainage characteristics, and this may be utilised to counteract the 'shine through' effect. The potential of [99mTc]Tilmanocept is of particular interest as it has a small molecular size of 7 nm facilitating rapid injection site clearance, and targets the CD206 receptor found on the reticuloendothelial cells in lymph nodes to promote accumulation within the SLN while reducing drainage to second tier nodes [21, 22]. A study assessing [99mTc]Tilmanocept in the setting of both OSCC and head and neck cutaneous SCC demonstrated a SLN detection rate of 97.6%, with a false negative rate of 2.56% [22]. This study included

