2899 - Re-Irradiation with SBRT of Locoregionally Recurrent or Second Primary Head and Neck Squamous Cell Carcinoma

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is an option for patients with locoregionally recurrent or second primary squamous cancers of the head and neck. To inform re-irradiation practice, we conducted a retrospective cohort study to evaluate survival and toxicity in patients receiving SBRT.

Materials/Methods: After IRB approval, an institutional database was queried for patients with locoregionally recurrent or second primary squamous cancers of the head and neck. Inclusion criteria included patients with prior radiotherapy of = 40 Gy to the head and neck who then received curative intent SBRT. Patient demographics, prior tumor/treatment, and current tumor/treatment factors were abstracted from the charts. Selected late (> 90 days post-treatment) toxicities were graded per the CTCAE Version 4. Locoregional control (LRC), progression free survival (PFS), and overall survival (OS) were measured from end of treatment and analyzed via Kaplan-Meier method. Potential prognostic factors were compared via log-rank method.

Results: This study included 94 patients available for analysis. The majority of patients in the cohort were male (74.5%) and had a previous history of smoking (54.3%). The most common location for tumors was in the oropharynx (36.2%), neck (20.2%), or oral cavity (19.2%), with recurrence comprising 71.2% of the cohort. When tested, HPV or EBV was positive in 51.2%. Median prescribed dose of SBRT was 40 Gy (18 – 40 Gy) in a median of 5 fractions (3-5 fractions). Concurrent systemic therapy was utilized in 33%, agents such as cisplatin, cetuximab, or immunotherapy were used. Median gross tumor volume was 11.68 cc (range 0.53 – 64.56 cc). Median follow up for patients alive at last contact was 35 months. Incidence of severe late toxicity (grade 3 or greater) was 22.3%. For the entire cohort, LRC at 24 months was 35.7%. On univariate analysis, patients with virally mediated disease (HPV or EBV+) or smaller tumors (=11.68 cc) had improved LRC at 2 years, 51.1% vs 8.5% (p<0.001) and 51.8% vs 14.8% (p<0.001), respectively. At 24 months, the rates of PFS, and OS for the entire cohort were 21.3%, and 34.6%, respectively.

Conclusion: Severe late toxicity and tumor control and survival outcomes for reirradiation with SBRT remain suboptimal. Patients with smaller tumors and/or virally mediated disease are more likely to have favorable outcomes. Further work is necessary to improve the therapeutic window for the complex treatment situation.