Adenoid cystic carcinoma of the head and neck: Patterns of recurrence and implications for intensity-modulated radiotherapy.

Background: We seek to inform radiotherapy (RT) delivery for adenoid cystic carcinoma of the head and neck (ACC) by evaluating RT techniques and recurrence patterns.
Methods: We identified patients with ACC treated with curative-intent RT from 2005 to 2021. Imaging was reviewed to determine local recurrence (LR).
Results: Ninety-one patients were included. The 5-year LR risk was 12.2% (6.6-22.7). One patient each experienced a marginal and out-of-field recurrence. Patients receiving >60 Gy postoperatively had a 5-year LR risk of 0% compared to 10.7% (4.2-27.2) with ≤60 Gy. Those receiving 70 and <70 Gy definitively had a 5-year LR risk of 15.2% (2.5-91.6) and 33.3% (6.7-100.0), respectively. No patients had regional nodal failure.
Conclusions: Modern, conformal RT for ACC results in low rates of LR. Doses >60 and 70 Gy may improve control in the postoperative and definitive settings, respectively. Elective nodal treatment can be omitted in well-selected patients.
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