Individualized prophylactic irradiation based on sentinel lymph node(s) identification in cN0 HNSCC

Purpose or Objective Due to a risk of occult nodal metastases in clinically node-negative (CN0) head and neck squamous cell carcinoma (HNSCC) patients, prophylactic and often bilateral neck irradiation is mandatory. However, it leads to a large irradiation of healthy tissue and could miss unexpected nodal basins drained by the tumor. This prospective, non-randomized, interventional phase II study investigated how sentinel lymph node (SLN) mapping by SPECT/CT may help to individualize prophylactic neck irradiation and its potential impact on radiation-related toxicities and tumor control. The final results are presented. Material and Methods Forty-four patients with newly diagnosed cN0 squamous cell carcinoma of the oral cavity, oropharynx, larynx or hypopharynx were included and treated with upfront (chemo)radiotherapy with a curative intent. After simulation, all patients were imaged in treatment position with SPECT/CT after 99mTc nanocolloid injection around the tumor. The neck levels containing up to four hottest SLN were selected for prophylactic irradiation (CTVn-LS). A comparative virtual planning was performed by including the levels selected on the basis of the current international guidelines (CTVn-IG). A radical identical dose was prescribed to the primary tumor. Both real and virtual treatments were calculated with RapidArc software by Varian¯. Dosimetric data to the different organs-at-risk (OAR) were compared between the two plans. Response was evaluated at 3 months by PET/CT. Follow-up neck CT scans were performed at 6, 12, 18 and 24 months. Results Lymphatic migration was observed in all of the 44 patients. Four patients (9%) presented a unpredicted lymphatic drainage and 21 patients (48%) had only a unilateral drainage. The volumes of CTVn-LS and PTVn-LS (median volumes of 91.8 cc and 219.1 cc, respectively) were systematically smaller than CTVn-LS and PTVn-IG (median volumes of 188.3 cc and 405.3 cc, respectively). This led to a significant dose decrease in identified OAR, particularly to the controlateral parotid gland, controlateral submandibular gland, inferior constrictor muscle for oral/oropharynx tumors and superior constrictor muscle for larynx/hypopharynx tumors (Table 1). At a median follow-up of 42 months, 3 patients experienced a regional relapse: 2 in an irradiated area (4.5%) and 1 in a non-irradiated area (2.3%). Currently, 4 patients had a local reccurence and 6 patients died (2 patients from geriatric degradation and 4 patients experienced fatal local relapse). [Table Presented] Conclusion SLN mapping using SPECT/CT allowed to significantly reduce the prophylactically irradiated neck volumes in cN0 HNSCC patients. This resulted in a significant dose decrease in OAR, especially in patients presenting a unilateral lymphatic drainage, while uncompromising the oncological outcome.