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Ipsilateral neck irradiation (INI) has been recommended for well lateralized early-stage tonsillar cancer. Also, more accurate staging tools and the chance of salvage surgery support the omission of elective contralateral neck irradiation. We aimed to clarify the indications for INI in patients with unilateral tonsillar cancer by comparing the outcomes of ipsilateral or bilateral neck irradiation (BNI).

Between January 2008 and March 2021, patients with pathologically confirmed unilateral tonsillar cancer who were treated with definitive radiotherapy (RT) at Asan Medical Center were reviewed retrospectively. The key inclusion criteria for INI were as follows: (1) primary tonsillar lesion which did not cross the midline (2) patients without lymph node (LN) metastasis or, if present, less than 6 cm. The radiation field was determined by the clinician, considering the extent of disease and the characteristics of each patient. Local recurrence (LR) was defined as disease progression in the RT field, and loco-regional recurrence (LRR) was defined as progression in the regional LN area or oropharynx outside the RT field. Within 3 months after the termination of RT, we reviewed acute toxicity based on the toxicity criteria of the Radiation Therapy Oncology Group.

A total of 93 patients were analyzed with median follow-up period of 60.5 months. Median age was 58 years (range, 35 – 86), and 79 (84.9%) patients were male. Eighteen (19.4%) patients underwent diagnostic tonsillectomy, and five (5.4%) patients underwent diagnostic LN excision before RT. Patients had T1 (n=17), T2 (n=46), or T3–4 (n=30) disease, with N0 (n=12), single node metastasis (n=18), or multiple nodes metastasis (n=63). The median total dose of 69.4 Gy (range, 55 – 71.8) was delivered with fraction of 1.8 – 2.3 Gy. Forty-eight (51.6%) patients received INI (Group 1) and 45 (48.4%) received BNI (Group 2). Evaluation was conducted until the best response, and ninety patients showed (96.8%) complete response after completion of RT. Two patients with partial response underwent additional neck dissection, and one with progressive disease received palliative treatment. The 2-year LR, LRR, distant metastasis control rates of Group 1 and Group 2 were 91% vs. 84.1%, 95.3% vs. 95.3%, and 95.7% vs. 86.4%, respectively (p=0.339, 1.000, 0.182). Contralateral neck node failure was observed in two patients in Group 1 and one patient in Group 2. The 2-year disease control rate and overall survival of Group 1 and Group 2 were 86.8% vs. 79.8%, 95.3% and 80.0%, respectively (p=0.451, 0.265). LR was the most common initial failure pattern in both groups. There was no significant difference in the incidence of acute toxicity between the two groups.

For patients with unilateral tonsillar cancer not crossing the midline, INI has been shown to yield high local control. Further studies with a large number of patients and longer follow-up periods will be needed to support this study in the future.