Stereotactic Body Radiation Therapy (SBRT) in Oropharynx and Oral Cavity Cancer: Toxicity and Local Control.

PURPOSE/OBJECTIVE(S) The purpose of the study is to assess the value of mucosal dosimetric parameters as predictors for severe radiation toxicity in patients with oral cavity and oropharynx cancer treated with SBRT MATERIALS/METHODS: All patients with oral cavity and oropharynx cancer who underwent SBRT between 2013 and 2020 were retrospectively reviewed. Primary endpoints were local control (LC) and grade > / = 3 toxicity potentially attributable to SBRT, based on CTCAE 5.0. The following parameters were analyzed as potential predictors of grade > / = 3 oral toxicity: ratio of total oral mucosal volume/oral mucosal volume outside of PTV, mean dose to oral mucosa, maximum dose to oral mucosa. Univariate and multivariate analyses were conducted to determine predictors of local failure (LF) and grade > / = 3 toxicity. Kaplan-Meier analysis was used to estimate LC. RESULTS A total of 54 tumors were treated in 49 individuals with a median age of 70 years. 38 (70.6%) of patients had oral cavity cancer and 16 (29.6%) had oropharynx cancer. Fifty-two (96.3%) tumors were squamous cell carcinoma. Median pain score at presentation was 3/10. 32 (59.3%) tumors were previously irradiated. Median PTV volume was 55 cc (range: 6.1cc-394 cc). Median prescribed radiation dose was 40 Gy given in 5 biweekly fractions. 40 patients received systemic therapy (platinum-based chemotherapy in 50% and cetuximab in 35% of patients). Oral pain nonsignificantly increased between 3 weeks and 3 months after starting treatment and subsequently returned to baseline after SBRT (P = 0.227). With median follow up of 10.5 months, local control (LC) was 67%. 1- and 2-year rates of LC in oral cavity tumors were 87.5% and 41.9% respectively. In oropharynx tumors, 1- and 2-year rates of LC were 74.3% and 49.5%. Grade > / = 3 toxicities were present in 16 (32.7%) patients that included osteonecrosis in 6 (12.2%) and ulceration or extensive tissue necrosis in 10 (20.4%). No significant relationship was present between mucosal surface radiation doses and acute oral mucosa toxicity. Univariate and analysis for both local control and grade > / = 3 toxicity did not find prior radiation, disease site, age, or PTV volume to be significantly associated. CONCLUSION SBRT provided comparable control and grade > / = 3 toxicity in the oropharynx and oral cavity, with numerically superior control in the oropharynx. No clear relationships were shown between volume of disease, mucosal surface radiation doses, retreatment, control and toxicity, though this analysis is limited by our sample size.