Head and Neck Stereotactic Body Radiation Therapy Re-Irradiation for Patients With Carotid or Skin Involvement Ineligible for RTOG 3507.

PURPOSE/OBJECTIVE(S) Patients with recurrent head and neck squamous cell carcinoma (HNSCC) who present with carotid encasement (CE) > 180˚, skin involvement and/or require bolus are not eligible for SBRT per RTOG 3507. The objective of this study was to characterize our institutional experience of SBRT for patients ineligible for RTOG 3507. MATERIALS/METHODS Patients with recurrent HNSCC treated with SBRT from 2010-2020 with a history of prior radiation were extracted from an IRB approved database. Patients were evaluated based on CE > 180˚ or ≤180˚ and if there was skin involvement and/or use of bolus. The primary outcome was incidence of treatment related carotid bleeding event (CBE) and skin toxicity after SBRT in the absence of disease. RESULTS Thirty-one patients were treated with SBRT to 37 sites with a median follow up of 8 months (mo) (range 2-47). The median time from prior radiation to SBRT was 13 mo (range 2-257). SBRT fractionation included 35 Gy (13%), 40 Gy (57%), and 45 Gy (30%) in 5 fractions. SBRT was delivered every other day (76%) or 2 fractions (24%) per week. Concurrent immunotherapy was given in 11% and cetuximab in 8%. A total of 30% (N = 11) of sites treated exhibited CE > 180˚ and 70% (N = 26) ≤180˚. There were no CBE related to SBRT, however 18% (N = 2) of patients with CE > 180˚ experienced fatal CBE related to progressive disease at 2.3 mo and 7.6 mo from SBRT. The risk of CBE was potentially related to CE > 180˚ (P = 0.08). Skin involvement and/or use of bolus was present in 43% (N = 16) of sites treated and absent in 57% (N = 21). The rate of treatment related skin toxicity was 19% (N = 3) and only occurred in those with pre-SBRT skin involvement and/or use of bolus. The cumulative incidence of treatment related skin toxicity at 3 mo and 6 mo was 13% (95% CI 1.9-33.6) and 27% (95% CI 4.0-58.8), respectively. Of the 3 treatment related skin toxicities there was one each of grade 2, 3, and 5. Grade 5 toxicity was related to untreated SBRT wound infection as the patient transitioned to hospice. The risk of treatment related skin toxicity was possibly related to pre-SBRT skin involvement and/or use of bolus (P = 0.007). Of the 13 sites with pre-SBRT skin involvement, 31% (N = 4) completely resolved, 54% (N = 7) had residual ulceration attributed to disease, and 15% (N = 2) had ulceration related to SBRT toxicity. The cumulative incidence of local failure at site of SBRT at 3 mo and 6 mo was 13% (95% CI 4-27.3) and 38% (95% CI 20.5-55.9), respectively. The median time of local and regional recurrence free survival were 7 and 5.5 mo, respectively. Median OS was 8 mo and the estimated 1-year OS was 25% (95% CI 9.9-40.9). CONCLUSION The risk of toxicity following SBRT for patients with > 180˚ CE, skin involvement and/or use of bolus appears to be largely related to persistent or recurrent disease. There were no CBE related to SBRT in the absence of disease and 31% of patients with pre-SBRT skin involvement exhibited complete healing after SBRT. Consideration of SBRT may still be beneficial for such patients with appropriate counselling.