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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.

Purpose/objective(s) Hypofractionated intensity modulated radiation therapy (H-IMRT) is uncommonly used in head and neck cancers due to concern for toxicity. This study reviews our experience using H-IMRT for head and neck cancers and explores its tolerability and efficacy. Materials/methods This single institution IRB approved retrospective study includes patients with head and neck cancers treated with definitive or post-operative H-IMRT from 2011-2020. Patients treated with ≥50Gy in 20 fractions to the primary tumor site and/or neck with at least 3 months of follow up were included. Patients treated to a superficial target only without proximity to mucosal surfaces or coverage of the elective neck (e.g., scalp; skin only targets) were excluded. Patients undergoing re-irradiation were excluded. Toxicity was scored using CTCAE v4.0. Acute toxicity included events occurring within 90 days of H-IMRT completion. Late toxicities occurred any time thereafter. Multiple toxicities in the same patient were scored separately. Results Fifty-nine patients with a median follow up of 10.9 months (range 3.0-111.5) were included. The majority of patients were white (93%) and male (78%) with a median age of 79.1. The most common primary tumor sites were skin (42%), major salivary glands (22%), and oral cavity (9%). The most frequent histologies included squamous cell carcinoma (66%) followed by thyroid cancer (7%), melanoma (5%), and Merkel cell carcinoma (5%). Treatment was delivered post-operatively in 80% and definitively in 20% of patients. All patients were treated with ≥50 Gy in 20 fractions, with the most common dose being 50 Gy (53%) followed by 55 Gy (44%). In 64% of patients a secondary elective dose of 45-50 Gy was used. Site treated included primary tumor site/bed with unilateral neck (54%), primary tumor site/bed with bilateral neck (19%), primary tumor site/bed alone (14%), unilateral neck (8%), and bilateral neck (5%). Five patients (8%) experienced a locoregional failure at a median time of 5.4 months (range 2.8-13.9). There were no grade 4 or 5 toxicities. Ten patients (17%) experienced acute grade 3 toxicity including mucositis (12%) and dermatitis (5%). Forty-six patients (78%) had an acute grade 2 toxicity, most commonly dermatitis (41%), pain (32%), fatigue (32%), dysgeusia (31%) and xerostomia (22%). Five patients (8%) experienced grade 2 late complications including neck fibrosis in three patients and trismus, aspiration pneumonia, and osteoradionecrosis in one patient each. No patient experienced grade 3 or higher late toxicity. No patients required the placement of a feeding tube or tracheostomy. Conclusion Hypofractionated IMRT in the definitive or post-operative treatment of head and neck cancers using ≥50Gy in 20 fractions appears safe and well tolerated with modest toxicity. Prospective studies comparing the safety and efficacy of H-IMRT to conventionally fractionated IMRT are warranted.