A Multi-Institutional Analysis of Outcomes following Stereotactic Body Radiation Therapy (SBRT) for Management of Metastases from Squamous Cell Carcinomas of the Head and Neck

Abstract

While increasing evidence supports the potential role of stereotactic body radiation therapy (SBRT) for oligometastatic disease, multi-institutional outcomes are limited for metastatic head and neck squamous cell carcinoma (mHNC). We screened a prospectively maintained international multi-institutional registry for mHNC patients treated with SBRT. Potential predictive factors of local control (LC), progression-free survival (PFS), and overall survival (OS) were evaluated with the Kaplan-Meier method and a Cox-proportional hazards model for multivariate analysis (MVA). Eighty-five patients with 102 lesions treated with SBRT were identified. Median patient age was 68 years, median KPS was 90%, and the median gross tumor volume (GTV) was 25cc. The median biologically effective dose (BED10) and dose/fraction were 82.75 Gy10 and 10 Gy, respectively. Commonly treated areas included the lung (51.8%), lymph node metastases (15.3%), and spine (14.1%), and common primary locations included the oral cavity (41.1%), larynx (24.7%), and oropharynx (23.5%). One- and 2-year OS rates were 62.7% and 40.7%, respectively. Patients with GTVs ≥ 25cc (77.4% vs. 58.2%; p = 0.02), those with non-lung metastases (67.5% vs. 58.2%; p = 0.07), lymph node metastases (43.3% vs. 66.6%; p = 0.10), spinal metastases (50% vs. 65.3%; p = 0.07), or KPS < 90% (42.2% vs.74.1%; p = 0.04) demonstrated inferior 1-year OS. On MVA, patients with spinal metastases (hazard ratio (HR) = 2.21 (95% CI: 1.07-4.60); p = 0.03)) were noted to have poorer OS in addition to those with GTVs ≥ 25cc (HR = 1.95 (95% CI: 0.93-4.09); p = 0.08). Utilizing KPS, GTV, and the presence of spinal metastases as potential prognostic indicators, 2-year OS rates were 81.2%, 32.6%, 38.2%, and not reached for patients with 0-3 of these factors, respectively (p = 0.0014). One-year and 2-year PFS rates were 72.5% and 60.6%, respectively, with superior 1-year PFS noted for patients of age < 70 (80.4% vs. 64.7%; p = 0.04) or with KPS ≥ 90% (78.3% vs. 61.5%; p = 0.03). One- and 2-year LC rates were 94.0% and 79.3%, respectively, with no prognostic or predictive factors relating to LC identified. Roughly 15% of patients reported toxicities, with no Grade 3 toxicities or association between dose and toxicities noted. To our knowledge, this represents the largest series of mHNC patients treated with SBRT. Patients with mHNC tolerated SBRT well without significant toxicities and encouraging LC. No significant dose-response for LC, PFS, OS, or toxicity was identified. When determining patient selection for aggressive local therapy in the setting of mHNC, KPS, GTV, and the presence of spinal metastases are potential prognostic factors to consider, particularly with regards to future clinical trial design.