Ipsilateral versus Bilateral Neck Radiation Therapy for Tonsillar Squamous Cell Carcinoma

Abstract

Ipsilateral neck radiation (I-RT) has been adopted for patients with early stage, well lateralized tonsillar squamous cell carcinoma (SCC), however there are limited data on outcomes of this approach in those with N2b disease. We report locoregional disease free survival (LR-DFS) for patients with tonsillar SCC who received I-RT or bilateral neck radiation (B-RT). Patients with tonsillar SCC who underwent definitive radiation, with or without chemotherapy, at a single academic institution between 3/1/90 and 10/15/18 were identified. Patient, tumor, and treatment characteristics were recorded. Stage was assigned per AJCC 7th ed. Wilcoxon Rank Sum and Chi-Square tests were used to compare patients who underwent either B-RT or I-RT. The primary outcome was locoregional disease-free survival (LR-DFS). Secondary outcomes were freedom from distant recurrence (FFDR) and overall survival (OS). Outcomes were estimated with Kaplan Meier method and compared via log rank test. Multivariate cox proportional hazards were used to estimate the effect of variables on endpoints. 216 patients with tonsillar SCC were treated with B-RT (n = 159) or I-RT (n = 57). Median age was 56 (IQR 51 – 64). Patients who underwent I-RT had T1 (45.6%) or T2 (54.4%) disease. Those who underwent B-RT had a higher proportion of T3/T4 disease: 8.2% T1, 25.8% T2, 42.8% T3, and 23.2% T4 disease (p<0.01). Most patients had nodal disease, I-RT: 3.5% N0, 19.3% N1, 14.0% N2a, 63.2% N2b and B-RT: 15.1% N0, 13.8% N1, 7.6% N2a, 36.5% N2b, 13.2% N2c, and 13.8% N3. HPV/p16 status for patients with B-RT was positive in 31.0%, negative in 2.0%, and unknown in 67.3%; for I-RT, HPV/p16 was positive in 59.6%, negative in 3.5%, and unknown in 36.8%. Median total dose to both groups was 70 Gy at 2 Gy/fraction. Concurrent chemotherapy was used in 94% of patients with B-RT and 77% with I-RT (p<0.01). 5-year estimates for survival endpoints are given below. On multivariate analysis controlling for T/N stage, use of chemotherapy, and HPV status, LR-DFS did not differ significantly for patients receiving B-RT versus I-RT (HR 0.67, 95% CI 0.40 – 4.10, p = 0.67). Among those treated with I-RT, 2 developed local recurrence at the primary tumor site. There were no ipsilateral or contralateral neck recurrences. Of 94 patients with N2b disease, 36 received I-RT. For those with N2b disease, 5-year LR-DFS was 93% (95% CI 73% – 98%) after I-RT versus 85% (95% CI 72% – 92%) after B-RT (p = 0.18). High rates of LR-DFS were achieved with I-RT for T1-T2 N0-2b tonsillar SCC, with no ipsilateral or contralateral neck recurrences. Use of I-RT did not compromise LR-DFS compared to B-RT. For patients with N2b disease, I-RT also resulted in high rates of LR-DFS. To our knowledge, this series represents the largest single institution cohort incorporating patients with tonsillar SCC and N2b disease treated with I-RT.Abstract 3868; TableB-RTI-RTLR-DFS (95% CI)78% (70-84%)91% (78-97%)FFDR (95% CI)89% (82-93%)96% (85-99%)OS (95% CI)71% (63-78%)91% (78-97%) Open table in a new tab